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

components/scheduler/child/scheduler_helper.h

Index: components/scheduler/child/scheduler_helper.h
diff --git a/components/scheduler/child/scheduler_helper.h b/components/scheduler/child/scheduler_helper.h
index 241ae609d166f65e94f60378014a46c7e3e4d44f..6cbae7afa07f80068e3ae40b7c71a4593b4029d6 100644
--- a/components/scheduler/child/scheduler_helper.h
+++ b/components/scheduler/child/scheduler_helper.h
@@ -5,6 +5,7 @@
 #ifndef COMPONENTS_SCHEDULER_CHILD_SCHEDULER_HELPER_H_
 #define COMPONENTS_SCHEDULER_CHILD_SCHEDULER_HELPER_H_
 
+#include "base/time/tick_clock.h"
 #include "components/scheduler/base/task_queue_manager.h"
 #include "components/scheduler/base/task_queue_selector.h"
 #include "components/scheduler/scheduler_export.h"
@@ -81,12 +82,11 @@ class SCHEDULER_EXPORT SchedulerHelper : public TaskQueueManager::Observer {
   void SetObserver(Observer* observer);
 
   // Accessor methods.
-  base::TimeTicks Now() const;
+  base::TickClock* tick_clock() const;
   base::TimeTicks NextPendingDelayedTaskRunTime() const;
   bool GetAndClearSystemIsQuiescentBit();
 
   // Test helpers.
-  void SetTimeSourceForTesting(scoped_ptr<base::TickClock> time_source);
   void SetWorkBatchSizeForTesting(size_t work_batch_size);
   TaskQueueManager* GetTaskQueueManagerForTesting();
 
@@ -100,8 +100,6 @@ class SCHEDULER_EXPORT SchedulerHelper : public TaskQueueManager::Observer {
   scoped_refptr<TaskQueue> control_after_wakeup_task_runner_;
   scoped_refptr<TaskQueue> default_task_runner_;
 
-  scoped_ptr<base::TickClock> time_source_;
-
   Observer* observer_;  // NOT OWNED
   const char* tracing_category_;
   const char* disabled_by_default_tracing_category_;