Make MemoryCoordinator and WebThreadSupportingGC usable from a worker thread.

This is necessary to support nested workers.

Bug: 829119
Change-Id: Ib48d10fc724477f720e77a15237ab106d8ed86f9
Reviewed-on: https://chromium-review.googlesource.com/1012794
Reviewed-by: Kenichi Ishibashi <bashi@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Nate Chapin <japhet@chromium.org>
Cr-Commit-Position: refs/heads/master@{#551389}
4 files changed