Move work signal count tracking from SequencedWorkerPool to the test file

Add OnHasWork() method to TestingObserver.

Make TestingObserver a constructor parameter, so it can
be read outside the lock.

BUG=117469
TEST=


Review URL: http://codereview.chromium.org/9689028

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@126780 0039d316-1c4b-4281-b951-d872f2087c98
3 files changed