Use SequenceChecker to allow Timer to run in SequencedWorkerPool

Timer was explicitly ensuring single-threaded usage by tracking the
thread used for scheduling tasks. Generalize that to ensure sequenced
task runner affinity via SequenceChecker, so it can be used by
SequencedWorkerPool threads.

BUG=552633

Review URL: https://codereview.chromium.org/1433373003

Cr-Commit-Position: refs/heads/master@{#365568}


CrOS-Libchrome-Original-Commit: ffa30fe7f5ec8b13c9e41d41d828e4fb8e67110b
3 files changed
tree: f18723210ddb956814115ea89809843044117fb9
  1. base/
  2. build/
  3. components/
  4. dbus/
  5. device/
  6. ipc/
  7. mojo/
  8. testing/
  9. third_party/
  10. ui/