Fixing and enhancing OrderedSimpleTaskRunner to allow 100% deterministic tests.

cc/test/scheduler_test_common.cc

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/test/scheduler_test_common.h"
 
 #include "base/logging.h"
 
 namespace cc {
 
 void FakeTimeSourceClient::OnTimerTick() {
   tick_called_ = true;
 }
 
 base::TimeTicks FakeDelayBasedTimeSource::Now() const { return now_; }
 
+base::TimeTicks TestScheduler::Now() const {
+  return test_task_runner_->Now();
+}
+
 }  // namespace cc