Revert of scheduler: Implement task observers

content/renderer/scheduler/task_queue_manager.h

Index: content/renderer/scheduler/task_queue_manager.h
diff --git a/content/renderer/scheduler/task_queue_manager.h b/content/renderer/scheduler/task_queue_manager.h
index 7a37385f64a30752776b2f24887748a9d0f99bc1..77bb2bfaf5c0a7cd48176118d0a307c6456021c8 100644
--- a/content/renderer/scheduler/task_queue_manager.h
+++ b/content/renderer/scheduler/task_queue_manager.h
@@ -9,7 +9,6 @@
 #include "base/debug/task_annotator.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
-#include "base/message_loop/message_loop.h"
 #include "base/pending_task.h"
 #include "base/single_thread_task_runner.h"
 #include "base/synchronization/lock.h"
@@ -91,11 +90,6 @@
   // tasks posted to the main loop. The batch size is 1 by default.
   void SetWorkBatchSize(int work_batch_size);
 
-  // These functions can only be called on the same thread that the task queue
-  // manager executes its tasks on.
-  void AddTaskObserver(base::MessageLoop::TaskObserver* task_observer);
-  void RemoveTaskObserver(base::MessageLoop::TaskObserver* task_observer);
-
   void SetTimeSourceForTesting(scoped_refptr<cc::TestNowSource> time_source);
 
  private:
@@ -161,8 +155,6 @@
 
   scoped_refptr<cc::TestNowSource> time_source_;
 
-  ObserverList<base::MessageLoop::TaskObserver> task_observers_;
-
   base::WeakPtrFactory<TaskQueueManager> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(TaskQueueManager);