Rewrite CancelableTaskTracker unit tests

Make it use TaskRunners and Closures instead of low-level synchronization
primitives.

Clean up death tests a bit.  In particular, remove a misleading one that was never fired (the one asserting that cancelling a non-existent ID should crash).

Add some ThreadChecker annotations to CancelableTaskTracker.

BUG=


Review URL: https://chromiumcodereview.appspot.com/11417077

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@169488 0039d316-1c4b-4281-b951-d872f2087c98
3 files changed