Revert of scheduler: Implement task observers

content/renderer/scheduler/renderer_scheduler.h

Index: content/renderer/scheduler/renderer_scheduler.h
diff --git a/content/renderer/scheduler/renderer_scheduler.h b/content/renderer/scheduler/renderer_scheduler.h
index 57d613eedf7c56ea2f0647880403fb0b8363deb4..6b4ecfaceef4fcd45bd998c5d288eed43c650371 100644
--- a/content/renderer/scheduler/renderer_scheduler.h
+++ b/content/renderer/scheduler/renderer_scheduler.h
@@ -66,14 +66,6 @@
   // Must be called from the main thread.
   virtual bool ShouldYieldForHighPriorityWork() = 0;
 
-  // Adds or removes a task observer from the scheduler. The observer will be
-  // notified before and after every executed task. These functions can only be
-  // called on the main thread.
-  virtual void AddTaskObserver(
-      base::MessageLoop::TaskObserver* task_observer) = 0;
-  virtual void RemoveTaskObserver(
-      base::MessageLoop::TaskObserver* task_observer) = 0;
-
   // Shuts down the scheduler by dropping any remaining pending work in the work
   // queues. After this call any work posted to the task runners will be
   // silently dropped.