Adds a flag to support "Virtual Time" to the blink scheduler

components/scheduler/base/lazy_now.cc

 // Copyright 2015 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 "components/scheduler/base/lazy_now.h"
 
 #include "components/scheduler/base/task_queue_manager.h"
 
 namespace scheduler {
 namespace internal {
 
 base::TimeTicks LazyNow::Now() {
   if (now_.is_null())
-    now_ = task_queue_manager_->Now();
+    now_ = tick_clock_->NowTicks();
   return now_;
 }
 
 }  // namespace internal
 }  // namespace scheduler