Now that we have an immutability bit, we can set the bit in object
header of newly allocated objects if those objects are always
deeply immutable.
That allows only checking for the immutable bit instead of checking
against a whole range of cids when sending objects via
`SendPort.send()` / `Isolate.exit()`.
TEST=ci
Change-Id: I4451a9fe11f68c7dd874d49ab632daa3102be19e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/281842
Commit-Queue: Martin Kustermann <kustermann@google.com>
Reviewed-by: Ryan Macnak <rmacnak@google.com>
Martin Kustermann
7db7bd0573