Fixing and enhancing OrderedSimpleTaskRunner to allow 100% deterministic tests.

cc/scheduler/scheduler.h

Index: cc/scheduler/scheduler.h
diff --git a/cc/scheduler/scheduler.h b/cc/scheduler/scheduler.h
index 3653c30cb014e0cce4e6d1c253eef9cc0d9c0ff2..52ff7a356df66d61309a0be5d01904faad87e59c 100644
--- a/cc/scheduler/scheduler.h
+++ b/cc/scheduler/scheduler.h
@@ -18,6 +18,7 @@
 #include "cc/scheduler/draw_result.h"
 #include "cc/scheduler/scheduler_settings.h"
 #include "cc/scheduler/scheduler_state_machine.h"
+#include "ui/gfx/frame_time.h"
 
 namespace base {
 class SingleThreadTaskRunner;
@@ -176,6 +177,9 @@ class CC_EXPORT Scheduler {
       int layer_tree_host_id,
       const scoped_refptr<base::SingleThreadTaskRunner>& impl_task_runner);
 
+  virtual base::TimeTicks Now() const;
+  virtual void SetupSyntheticBeginFrames();
+
   const SchedulerSettings settings_;
   SchedulerClient* client_;
   int layer_tree_host_id_;
@@ -221,7 +225,6 @@ class CC_EXPORT Scheduler {
   bool CanCommitAndActivateBeforeDeadline() const;
   void AdvanceCommitStateIfPossible();
   bool IsBeginMainFrameSentOrStarted() const;
-  void SetupSyntheticBeginFrames();
 
   base::WeakPtrFactory<Scheduler> weak_factory_;