CL: https://codereview.chromium.org/2490113002/

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/fb4c1fe6ad37005d9818c65a42728ac7179bf499

commit fb4c1fe6ad37005d9818c65a42728ac7179bf499
Author: nhiroki <nhiroki@chromium.org>
Date: Fri Nov 11 14:35:21 2016

Worker: Replace CancellableTaskFactory with postDelayedCancellableTask

Before this CL, WorkerThread::ForceTerminationTask is implemented with
CancellableTaskFactory that is deprecated in favor of
WebTaskRunner::post(Delayed)CancellableTask.

This CL removes ForceTerminationTask/CancellableTaskFactory, and instead
implements the same functionality with postDelayedCancellableTask.

BUG= 663624 

Review-Url: https://codereview.chromium.org/2490113002
Cr-Commit-Position: refs/heads/master@{#431559}

[modify] https://crrev.com/fb4c1fe6ad37005d9818c65a42728ac7179bf499/third_party/WebKit/Source/core/workers/WorkerThread.cpp
[modify] https://crrev.com/fb4c1fe6ad37005d9818c65a42728ac7179bf499/third_party/WebKit/Source/core/workers/WorkerThread.h
[modify] https://crrev.com/fb4c1fe6ad37005d9818c65a42728ac7179bf499/third_party/WebKit/Source/core/workers/WorkerThreadTest.cpp