TaskScheduler: Add SequenceToken and ScopedSetSequenceTokenForCurrentThread.
base::SequenceToken is an opaque token that identifies a series of
sequenced tasks. base::internal::ScopedSetSequenceTokenForCurrentThread
identifies the SequenceToken of tasks running on the current thread
throughout its lifetime.
This CL also changes SequenceChecker to support
base::internal::SequenceToken.
In an upcoming CL, base/task_scheduler will tag all its sequences with
a token returned by SequenceToken::Create(). Before running a task, it
will instantiate a ScopedSetSequenceTokenForCurrentThread with the
SequenceToken of the task's sequence.
Sample usage of SequenceToken in follow-up CL:
https://codereview.chromium.org/2172713003/
BUG=553459
Review-Url: https://codereview.chromium.org/2165663003
Cr-Commit-Position: refs/heads/master@{#407937}
10 files changed
