- Initial and final marking no longer visit all of new-space, reducing the STW pause for major GC.
- A scavenge during concurrent marking must forward / filter objects in the marking worklist that are moved / collected, increasing the STW pause for minor GC.
- Unreachable intergenerational cycles and weak references are collected in the next mark-sweep instead of first requiring enough scavenges to promote the whole cycle or weak target into old-space.
- Artificial minor GCs are no longer needed to avoid memory leaks from back-to-back major GCs.
- reachabilityBarrier is now just a count of major GCs.
TEST=ci
Change-Id: Ic7754e8d972763654eae2b7faa8670735d9cda3f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/340644
Reviewed-by: Siva Annamalai <asiva@google.com>
Commit-Queue: Ryan Macnak <rmacnak@google.com>
This reverts commit 5daaa7d9eb.
Reason for revert: internal crashes
Original change's description:
> [vm, gc] Mark through new-space.
>
> - Initial and final marking no longer visit all of new-space, reducing the STW pause for major GC.
> - A scavenge during concurrent marking must forward / filter objects in the marking worklist that are moved / collected, increasing the STW pause for minor GC.
> - Unreachable intergenerational cycles and weak references are collected in the next mark-sweep instead of first requiring enough scavenges to promote the whole cycle or weak target into old-space.
> - Artificial minor GCs are no longer needed to avoid memory leaks from back-to-back major GCs.
> - reachabilityBarrier is now just a count of major GCs.
>
> TEST=ci
> Change-Id: I4a6a23273d8ecb78c640f054731d4ceb737bfc4d
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/325840
> Reviewed-by: Siva Annamalai <asiva@google.com>
> Commit-Queue: Ryan Macnak <rmacnak@google.com>
Change-Id: I8a50074db343c63c14f0487ae8b4f5fee2c4ae76
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/330720
Reviewed-by: Ryan Macnak <rmacnak@google.com>
Commit-Queue: Slava Egorov <vegorov@google.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
- Initial and final marking no longer visit all of new-space, reducing the STW pause for major GC.
- A scavenge during concurrent marking must forward / filter objects in the marking worklist that are moved / collected, increasing the STW pause for minor GC.
- Unreachable intergenerational cycles and weak references are collected in the next mark-sweep instead of first requiring enough scavenges to promote the whole cycle or weak target into old-space.
- Artificial minor GCs are no longer needed to avoid memory leaks from back-to-back major GCs.
- reachabilityBarrier is now just a count of major GCs.
TEST=ci
Change-Id: I4a6a23273d8ecb78c640f054731d4ceb737bfc4d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/325840
Reviewed-by: Siva Annamalai <asiva@google.com>
Commit-Queue: Ryan Macnak <rmacnak@google.com>
This reverts commit 3fb88e4c66.
Reason for revert: b/297175670
Original change's description:
> [vm, gc] Mark through new-space.
>
> - Initial and final marking no longer visit all of new-space, reducing the STW pause for major GC.
> - A scavenge during concurrent marking must forward / filter objects in the marking worklist that are moved / collected, increasing the STW pause for minor GC.
> - Unreachable intergenerational cycles and weak references are collected in the next mark-sweep instead of first requiring enough scavenges to promote the whole cycle or weak target into old-space.
> - Artificial minor GCs are no longer needed to avoid memory leaks from back-to-back major GCs.
> - reachabilityBarrier is now just a count of major GCs.
>
> TEST=ci
> Change-Id: I6362802cd93ba5ba9c39f116ddff82e4feb4c312
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/321304
> Commit-Queue: Ryan Macnak <rmacnak@google.com>
> Reviewed-by: Siva Annamalai <asiva@google.com>
Change-Id: I33075156160dc35861355d738a5776b74dce88b9
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/322344
Reviewed-by: Martin Kustermann <kustermann@google.com>
Auto-Submit: Ivan Inozemtsev <iinozemtsev@google.com>
Commit-Queue: Martin Kustermann <kustermann@google.com>
- Initial and final marking no longer visit all of new-space, reducing the STW pause for major GC.
- A scavenge during concurrent marking must forward / filter objects in the marking worklist that are moved / collected, increasing the STW pause for minor GC.
- Unreachable intergenerational cycles and weak references are collected in the next mark-sweep instead of first requiring enough scavenges to promote the whole cycle or weak target into old-space.
- Artificial minor GCs are no longer needed to avoid memory leaks from back-to-back major GCs.
- reachabilityBarrier is now just a count of major GCs.
TEST=ci
Change-Id: I6362802cd93ba5ba9c39f116ddff82e4feb4c312
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/321304
Commit-Queue: Ryan Macnak <rmacnak@google.com>
Reviewed-by: Siva Annamalai <asiva@google.com>
This reverts commit e95e7b8e96.
Reason for revert: suspected cause to non-deterministic AOT binaries crashes, b/296014654
Original change's description:
> [vm, gc] Mark through new-space.
>
> - Initial and final marking no longer visit all of new-space, reducing the STW pause for major GC.
> - A scavenge during concurrent marking must forward / filter objects in the marking worklist that are moved / collected, increasing the STW pause for minor GC.
> - Unreachable intergenerational cycles and weak references are collected in the next mark-sweep instead of first requiring enough scavenges to promote the whole cycle or weak target into old-space.
> - Artificial minor GCs are no longer needed to avoid memory leaks from back-to-back major GCs.
> - reachabilityBarrier is now just a count of major GCs.
>
> TEST=ci
> Change-Id: I8c2c64b120766571b62d3bd8dab37ae81c2dca98
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/319583
> Commit-Queue: Ryan Macnak <rmacnak@google.com>
> Reviewed-by: Siva Annamalai <asiva@google.com>
Change-Id: Idda542c7c657d4f14c836423b173c9b067132212
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/320820
Reviewed-by: Martin Kustermann <kustermann@google.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Ilya Yanok <yanok@google.com>
- Initial and final marking no longer visit all of new-space, reducing the STW pause for major GC.
- A scavenge during concurrent marking must forward / filter objects in the marking worklist that are moved / collected, increasing the STW pause for minor GC.
- Unreachable intergenerational cycles and weak references are collected in the next mark-sweep instead of first requiring enough scavenges to promote the whole cycle or weak target into old-space.
- Artificial minor GCs are no longer needed to avoid memory leaks from back-to-back major GCs.
- reachabilityBarrier is now just a count of major GCs.
TEST=ci
Change-Id: I8c2c64b120766571b62d3bd8dab37ae81c2dca98
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/319583
Commit-Queue: Ryan Macnak <rmacnak@google.com>
Reviewed-by: Siva Annamalai <asiva@google.com>
This reverts commit 6194209b28.
Reason for revert: issues on arm32
Original change's description:
> [vm, gc] Mark through new-space.
>
> - Initial and final marking no longer visit all of new-space, reducing the STW pause for major GC.
> - A scavenge during concurrent marking must forward / filter objects in the marking worklist that are moved / collected, increasing the STW pause for minor GC.
> - Unreachable intergenerational cycles and weak references are collected in the next mark-sweep instead of first requiring enough scavenges to promote the whole cycle or weak target into old-space.
> - Artificial minor GCs are no longer needed to avoid memory leaks from back-to-back major GCs.
> - reachabilityBarrier is now just a count of major GCs.
>
> TEST=ci
> Change-Id: I3668a2e56821f9eadf96e38c228dab27be656016
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/309826
> Reviewed-by: Siva Annamalai <asiva@google.com>
> Commit-Queue: Ryan Macnak <rmacnak@google.com>
Change-Id: I434eb595c9e7858efc8c9b07cbca954e5649f506
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/319321
Commit-Queue: Ryan Macnak <rmacnak@google.com>
Reviewed-by: Siva Annamalai <asiva@google.com>
- Initial and final marking no longer visit all of new-space, reducing the STW pause for major GC.
- A scavenge during concurrent marking must forward / filter objects in the marking worklist that are moved / collected, increasing the STW pause for minor GC.
- Unreachable intergenerational cycles and weak references are collected in the next mark-sweep instead of first requiring enough scavenges to promote the whole cycle or weak target into old-space.
- Artificial minor GCs are no longer needed to avoid memory leaks from back-to-back major GCs.
- reachabilityBarrier is now just a count of major GCs.
TEST=ci
Change-Id: I3668a2e56821f9eadf96e38c228dab27be656016
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/309826
Reviewed-by: Siva Annamalai <asiva@google.com>
Commit-Queue: Ryan Macnak <rmacnak@google.com>
An embedder (or the VM) can exit an isolate via `Thread::ExitIsolate()`
at a point where there's still active state (e.g. dart frames).
Because of this the VM has so far conservatively retained the [Thread]
object of dart mutators throughout the isolate's lifetime. After which
is was manually `delete`ed. We'd never re-use those [Thread] objects (we
do re-use [Thread] objects of non-dart-mutator threads).
When exiting via `Thread::ExitIsolate()` with active state, the mutator
was assumed to be at-safepoint at all levels. It was removed from the
thread registry's active threads. This also means that when e.g. GC runs
it can't use the thread registry to find all active threads it may
need to scan, instead it uses [Isolate::mutator_thread_] of all isolates.
This causes a variety of subtle issues, but the main one that motivated
this change is the following:
If a thread obtains a safepoint operation it means all other mutators
are parked. The thread owning the safepoint can do whatever it likes.
When introducing reload operation safepoints, a thread may want to
ReloadSafepointOperation reload(thread);
...
// Compile sources.
{
TransitionVMToNative transition(thread);
// Will temporarily exit & re-enter current isolate.
response_port = Dart_NewNativePort();
Dart_PostCObject(kernel_isolate_port, ...);
// Wait on [response_port] for response.
}
This will cause the reloading thread to own the reload safepoint
operation but still transition states and even exit/re-enter the
isolate. Though this is currently not possible in the way enter/exit is
implemented.
So we'll refactor this fragile code in the following way:
* Move thread enter/exit logic entirely to the [Thread] object.
* Keep used threads in the thread registry's active list.
=> This allows us to keep various state on the [Thread] and thereby
avoids clearing it when suspending & re-initialing it when resuming
=> It makes nested `Thread::ExitIsolate()` faster as we mainly have
to enter safepoint (avoid acquiring threads lock, avoid releasing
storebuffers, ...)
=> It makes nested `Thread::EnterIsolate()` faster as we mainly have
to leave the safepoint (avoid acquiring threads lock, avoid acquiring
storebuffers, ...).
=> A mutator can now own a safepoint operation (e.g. reload safepoint
operation) and still `ExitSafepoint()` / `EnterSafepoint()` safely -
as those are based on the normal `EnterSafepoint()` and
`LeaveSafepoint()` APIs.
* We separate
- Suspend & Resume of a dart mutator (possibly with active stack)
- Setup & Reset of state only relevant for dart mutators
- Setup & Reset of state relevant for any mutator
* We unify how the [Thread] objects are freed between dart mutator and
non-dart mutators: [Thread] objects without state can be given back to
the [ThreadRegistry] and re-used (instead of being deleted in
`Isolate::~Isolate`)
* We have capability to free [Thread] objects if a dart mutator has an
empty stack & re-use for another isolate of the same group.
(In future we may have N Thread objects for N cores and the threads
would even maintain their TLABs when switching between isolates)
* Since we allow reusing of [Thread] objects also for dart mutators now,
we have extensive asserts to ensure they are "clean" when they get
into the free list and come out "clean" again.
TEST=ci
Change-Id: Id85e8e484efd98d28e323b33795716420e619986
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/296585
Reviewed-by: Ryan Macnak <rmacnak@google.com>
Commit-Queue: Martin Kustermann <kustermann@google.com>
Some cleanups factored out of a larger CL (which refactors enter/exit of threads):
* remove unused `#include "vm/thread_registry.h"`
* remove unused/unnecessary fields from [Thread] object
* rename IsMutator() -> IsDartMutator()
* make tests using setjmp() drain the sticky error
=> to ensure there's no sticky error on isolate shutdown
TEST=ci
Change-Id: I53935e8bd0628ab3768627d6d5e01c3f0e3a57ad
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/296582
Commit-Queue: Martin Kustermann <kustermann@google.com>
Reviewed-by: Alexander Aprelev <aam@google.com>
This CL introduces new embedding APIs for supporting heap sample
profiling. A registered sampling callback is invoked approximately every
N bytes based on an exponential distribution, providing information
about the isolate group the allocation occurred in, the user visible
name of the allocated object type, a weak persistent handle to the
allocated object, and the size of the allocation.
Sampling is triggered using artificial TLAB boundaries to cause
allocations to be sampled to take the allocation slow path where the
registered callback can be invoked with the allocation information.
Only new space allocations are currently traced, with old space
allocation support to be added in a future CL.
TEST=Dart_HeapSampling
Change-Id: I22bcdeec6e823bc1ab44898d4c596fbed7169fa1
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/264520
Commit-Queue: Ben Konyi <bkonyi@google.com>
Reviewed-by: Siva Annamalai <asiva@google.com>
Reviewed-by: Ryan Macnak <rmacnak@google.com>
This CL:
* Moves [Heap]/[SharedClassTable] from [Isolate] to [IsolateGroup], which
will make all isolates in the group use the same heap. The GC will use
the shared class table for object size information.
* Adds support for entering/leaving an isolate group as a helper thread
(e.g. via [Thread::EnterIsolateGroupAsHelper]). The current active
isolate group can be accessed via TLS `IsolateGroup::Current()` or
`Thread::isolate_group_`. When entering as a helper thread there will be
no current isolate.
* Changes the GC to use the above mechanism and ensures GC works without
a currently active isolate. The GC will use information purely available via
[IsolateGroup]. The GC will iterate all isolates within an isolate
group e.g. for scanning roots.
* Makes spawning of new isolates start in their own isolate group.
Once the isolate is fully functional it's heap will be merged into
the original isolate group
* Moves ApiState, containing persistent and weak persistent handles,
from [Isolate] to [IsolateGroup], plus adds appropriate locking.
Issue https://github.com/dart-lang/sdk/issues/36097
Change-Id: Ia8e1d8aa78750e8400864200f4825395a182c004
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/126646
Commit-Queue: Martin Kustermann <kustermann@google.com>
Reviewed-by: Ryan Macnak <rmacnak@google.com>
This CL moves the thread registry and the safepoint handler to the
[IsolateGroup]. This will cause all threads belonging to the isolate
group to safepoint together.
=> We will therefore start to get an idea of the impact this will have on
pause times.
So far it was only possible to enter a particular isolate (e.g. as mutator
thread or auxiliary thread). This CL adds support for entering an isolate
group (instead of a particular isolate) as an auxiliarly thread. The
current isolate group is available via `IsolateGroup::Current()`.
=> This is a preparation step to let GC threads enter the isolate
group as auxiliary threads, not associated with a particular isolate but
to an isolate group as a whole.
Issue https://github.com/dart-lang/sdk/issues/36097
Change-Id: I7069d07130938d370869f02060570143bfeb1b48
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/108801
Reviewed-by: Ryan Macnak <rmacnak@google.com>
Commit-Queue: Martin Kustermann <kustermann@google.com>
The thread registry is creating [Thread] objects when threads enter an
isolate (as mutator or helper). Once threads exit an isolate, the
[Thread] structure is returned and the thread registry will put it
into a cache for later re-use.
The mutator [Thread] object is an exception: Exiting and entering the
isolate as mutator will always use the same cached [Thread] object.
We want to eventually use one thread registry for an entire isolate
group. There will therefore be multiple mutator threads per thread registry.
We therefore move the cached mutator thread from the thread registry to the
[Isolate] object.
Issue https://github.com/dart-lang/sdk/issues/36097
Change-Id: Id27dff886d79ca76f6e05320151aeb72c8ba5140
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/108720
Commit-Queue: Martin Kustermann <kustermann@google.com>
Reviewed-by: Ryan Macnak <rmacnak@google.com>
In many cases, the Mutexes and Monitors have to be marked "mutable"
because they're used to synchronize const accessor methods.
Small text segment improvement for Product builds:
$ size dart.{arm,x64}.{before,after}
text data bss dec hex filename
19726069 409960 392332 20528361 1393ce9 dart.arm.before
19725525 409960 392332 20527817 1393ac9 dart.arm.after
22576021 600376 1782824 24959221 17cd8f5 dart.x64.before
22574821 600376 1782824 24958021 17cd445 dart.x64.after
Change-Id: I68f5cd5ad452044df8bfebd160910496036a3e6b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/101745
Commit-Queue: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Vyacheslav Egorov <vegorov@google.com>
- Introduce a slimmed down version of thread.h, which just depends on the
Zone and StackResource.
- Introduce a layering check that would prevent the coupling in the future.
This is the first step towards decoupling compiler from runtime.
There are multiple reasons to introduce the decoupling but the main
reason currently is to introduce a controlled surface through which
compiler reaches into runtime to catch any places where runtime word size
might influence the compiler and then enable building compiler that
targets 32-bit runtime but is embedded into a 64-bit runtime.
Issue https://github.com/dart-lang/sdk/issues/31709
Change-Id: Id63ebbaddca55dd097298e51c90d957a73fa476e
Reviewed-on: https://dart-review.googlesource.com/c/87182
Commit-Queue: Vyacheslav Egorov <vegorov@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>
The mutator thread structure is kept alive until the death of the
isolate. Yet the mutator thread does not have to be scheduled all the
time. A native call, for example, can suspend the isolate via
Dart_ExitIsolate to perform other work.
This particular flaky crash had precisely this problem: The mutator
thread suspended itself with an IsolateSaver scope (which uses Dart_ExitIsolate)
and invoked Dart_NewNativePort. While at the same time the background
compiler for that isolate triggered an oldspace allocation, which
triggered a marking task. The marker task needs to traverses the mutator
stack and hits a frame with a deoptimization marker, which causes it to
access the mutator thread's isolate pointer, which was incorrectly NULL.
Fixes https://github.com/dart-lang/sdk/issues/34748
Fixes https://github.com/dart-lang/sdk/issues/34323
Change-Id: I80440856f72b3c194a516084ddc254b2e56740d8
Reviewed-on: https://dart-review.googlesource.com/c/80860
Reviewed-by: Vyacheslav Egorov <vegorov@google.com>
Commit-Queue: Martin Kustermann <kustermann@google.com>
Previously there were places in the code where an API accepted a
`bool validate_frames` and call sites passed an enum value (which
implicitly got converted to a bool).
By changing the APIs to require an enum, the compiler will tell us if a
caller doesn't pass one.
Change-Id: I29fcd0b018e6cdd7e00b5bb03e83b9636d1345d4
Reviewed-on: https://dart-review.googlesource.com/57823
Commit-Queue: Martin Kustermann <kustermann@google.com>
Reviewed-by: Régis Crelier <regis@google.com>
This is a fixed version of c84f30741c90d040254767ff769a40d2cba3fb1a that
resolves issues with comparing uint and intptr_t.
Original Commit Message:
Added tracking of memory usage inside of threads. In addition, the max memory usage is kept track of using a high watermark for both the threads and the isolates. Isolate high watermark information is updated when a thread exits the isolate. The isolate high watermark consists of the sum of all thread high watermarks (including the high watermark of the exiting thread). High watermark information for both threads and isolates is now visible in the isolate view in the Observatory.
BUG=
R=johnmccutchan@google.com
Review-Url: https://codereview.chromium.org/2610253002 .
Added tracking of memory usage inside of threads. In addition, the max memory usage is kept track of using a high watermark for both the threads and the isolates. Isolate high watermark information is updated when a thread exits the isolate. The isolate high watermark consists of the sum of all thread high watermarks (including the high watermark of the exiting thread). High watermark information for both threads and isolates is now visible in the isolate view in the Observatory.
BUG=
R=johnmccutchan@google.com
Review-Url: https://codereview.chromium.org/2609253002 .
Added methods to surface number of zone and scoped handles in each isolate. These values are displayed in the isolate view page in the Observatory. These handle counts for the native IO isolate will be surfaced in another CL.
BUG=
R=asiva@google.com
Review-Url: https://codereview.chromium.org/2601153002 .
Added tracking of memory usage inside of threads. In addition, the max memory usage is kept track of using a high watermark for both the threads and the isolates. Isolate high watermark information is updated when a thread exits the isolate. The isolate high watermark consists of the sum of all thread high watermarks (including the high watermark of the exiting thread). High watermark information for both threads and isolates is now visible in the isolate view in the Observatory.
BUG=
R=asiva@google.com
Review-Url: https://codereview.chromium.org/2608463002 .
- uses thread execution status transition to track when a thread is in a safepoint or needs to block for a safepoint
- introduces a monitor per Thread object
- uses a per thread safepoint handshake between the thread requesting a safepoint and the requested thread.
The ThreadRegistry class now contains only the thread list for an isolate and the functionality of scheduling a thread onto an Isolate and unscheduling it from teh isolate. We could fold this functionality into the Isolate class in a different CL.
R=rmacnak@google.com, zra@google.com
Review URL: https://codereview.chromium.org/1541073002 .
- Ensure that no new OSThreads are created once the VM is in shutdown mode
- Do not query thread_list_head_ without a lock (this leads to the race which causes two threads to delete the lock and TLS at the same time)
BUG=25236
R=zra@google.com
Review URL: https://codereview.chromium.org/1537543002 .
The profile signal handler may interrupt when the current Thread
is in an inconsistent state.
Members of the Thread that is unscheduled are NULLed out before
OSThread::SetCurrent sets a new current Thread. Fix this by resetting
the current Thread's fields after a new Thread is set as current.
BUG=#25702
R=iposva@google.com
Review URL: https://codereview.chromium.org/1491283002 .
fields in a thread (i.e fields that are not Dart VM related)
- Split the Thread structure to be a pure Dart per thread structure and add
a pointer to os_thread which points to the OSThread structure
- Change Schedule/UnSchedule to set the Dart Thread structure as the TLS of
the thread when it is inside the Dart world and reset the TLS back to the
OSThread strcuture when is exits the Dart World.
- Moved the stack_base and few stack size related functions to OSThread from Isolate
R=johnmccutchan@google.com, zra@google.com
Review URL: https://codereview.chromium.org/1439483003 .
Now that we have a central list of all threads that are interacting with the VM we can stop relying on the Isolate's thread registry to cache timeline blocks.
- Move from caching blocks in the Isolate's thread registry and caching them in the Thread directly.
- This allows cached blocks to have events from multiple isolates, increasing usage density and reducing the number of blocks being cached at any given time.
- We no longer need a distinct global block, this allows me to remove a bunch of dead code.
R=turnidge@google.com
Review URL: https://codereview.chromium.org/1402383003 .
- Add Timeline::ReclaimAllBlocks and Timeline::ReclaimIsolateBlocks utility functions to ensure that all cached blocks are closed before reporting the timeline
- Adjust Timeline_Dart_GlobalTimelineGetTrace to exercise block reclaiming
- Add ability to reclaim blocks from threads entered into an isolate
- Fix IsolateTimelineEventFilter to actually filter out open blocks
- Make some existing tests call Timeline::ReclaimIsolateBlocks before reporting
- Added implementation and locking notes to timeline.cc
R=turnidge@google.com
Review URL: https://codereview.chromium.org//1363033003 .
Ryan Macnak