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

components/scheduler/renderer/renderer_scheduler_impl.h

Index: components/scheduler/renderer/renderer_scheduler_impl.h
diff --git a/components/scheduler/renderer/renderer_scheduler_impl.h b/components/scheduler/renderer/renderer_scheduler_impl.h
index d137b16f6d7692670a55f42fc4d5b7dc8194ded6..ad30786bec17dd9c50d71cc1a96d89277a756b1e 100644
--- a/components/scheduler/renderer/renderer_scheduler_impl.h
+++ b/components/scheduler/renderer/renderer_scheduler_impl.h
@@ -33,8 +33,11 @@ class SCHEDULER_EXPORT RendererSchedulerImpl
       public SchedulerHelper::Observer,
       public RenderWidgetSignals::Observer {
  public:
+  enum class TimeSource { NORMAL, VIRTUAL };
+
   RendererSchedulerImpl(
-      scoped_refptr<SchedulerTaskRunnerDelegate> main_task_runner);
+      scoped_refptr<SchedulerTaskRunnerDelegate> main_task_runner,
+      TimeSource time_source);
   ~RendererSchedulerImpl() override;
 
   // RendererScheduler implementation:
@@ -71,6 +74,8 @@ class SCHEDULER_EXPORT RendererSchedulerImpl
   void SuspendTimerQueue() override;
   void ResumeTimerQueue() override;
   void SetTimerQueueSuspensionWhenBackgroundedEnabled(bool enabled) override;
+  double currentTime() const override;
+  double monotonicallyIncreasingTime() const override;
 
   // RenderWidgetSignals::Observer implementation:
   void SetAllRenderWidgetsHidden(bool hidden) override;
@@ -241,12 +246,14 @@ class SCHEDULER_EXPORT RendererSchedulerImpl
   CancelableClosureHolder end_renderer_hidden_idle_period_closure_;
   CancelableClosureHolder suspend_timers_when_backgrounded_closure_;
 
+  const TimeSource time_source_;
+
   // We have decided to improve thread safety at the cost of some boilerplate
   // (the accessors) for the following data members.
 
   struct MainThreadOnly {
-    explicit MainThreadOnly(
-        const scoped_refptr<TaskQueue>& compositor_task_runner);
+    MainThreadOnly(const scoped_refptr<TaskQueue>& compositor_task_runner,
+                   base::TickClock* time_source);
     ~MainThreadOnly();
 
     TaskCostEstimator loading_task_cost_estimator;