Output TimelineEventBlocks in sorted order

- Before outputting to JSON sort TimelineEventBlocks by earliest event time.
- Output using sorted block order.
- Works around a bug in mojo (https://github.com/domokit/mojo/issues/649)

R=zra@google.com

Review URL: https://codereview.chromium.org/1657843003 .

runtime/vm/timeline.cc

@@ -721,6 +721,7 @@ void TimelineBeginEndScope::EmitBegin() {
   TimelineEvent* event = stream()->StartEvent();
   if (event == NULL) {
     // Stream is now disabled.
+    set_enabled(false);
     return;
   }
   ASSERT(event != NULL);
@@ -737,6 +738,7 @@ void TimelineBeginEndScope::EmitEnd() {
   TimelineEvent* event = stream()->StartEvent();
   if (event == NULL) {
     // Stream is now disabled.
+    set_enabled(false);
     return;
   }
   ASSERT(event != NULL);
@@ -1160,17 +1162,35 @@ TimelineEventBlock* TimelineEventEndlessRecorder::GetNewBlockLocked() {
   return head_;
 }
 
+static int TimelineEventBlockCompare(TimelineEventBlock* const* a,
+                                     TimelineEventBlock* const* b) {
+  return (*a)->LowerTimeBound() - (*b)->LowerTimeBound();
+}
+
 
 void TimelineEventEndlessRecorder::PrintJSONEvents(
     JSONArray* events,
     TimelineEventFilter* filter) {
   MutexLocker ml(&lock_);
+  // Collect all interesting blocks.
+  MallocGrowableArray<TimelineEventBlock*> blocks(8);
   TimelineEventBlock* current = head_;
   while (current != NULL) {
-    if (!filter->IncludeBlock(current)) {
-      current = current->next();
-      continue;
+    if (filter->IncludeBlock(current)) {
+      blocks.Add(current);
     }
+    current = current->next();
+  }
+  // Bail early.
+  if (blocks.length() == 0) {
+    return;
+  }
+  // Sort the interesting blocks so that blocks with earlier events are
+  // outputted first.
+  blocks.Sort(TimelineEventBlockCompare);
+  // Output blocks in sorted order.
+  for (intptr_t block_idx = 0; block_idx < blocks.length(); block_idx++) {
+    current = blocks[block_idx];
     intptr_t length = current->length();
     for (intptr_t i = 0; i < length; i++) {
       TimelineEvent* event = current->At(i);
@@ -1180,7 +1200,6 @@ void TimelineEventEndlessRecorder::PrintJSONEvents(
         events->AddValue(event);
       }
     }
-    current = current->next();
   }
 }
 

runtime/vm/timeline.h

@@ -94,7 +94,6 @@ class TimelineEvent {
   // Keep in sync with StateBits below.
   enum EventType {
     kNone,
-    kSerializedJSON,  // Events from Dart code.
     kBegin,
     kEnd,
     kDuration,
@@ -387,6 +386,10 @@ class TimelineEventScope : public StackResource {
     return enabled_;
   }
 
+  void set_enabled(bool enabled) {
+    enabled_ = enabled;
+  }
+
   const char* label() const {
     return label_;
   }