Revert of scheduler: Implement task observers

content/renderer/scheduler/task_queue_manager.cc

Index: content/renderer/scheduler/task_queue_manager.cc
diff --git a/content/renderer/scheduler/task_queue_manager.cc b/content/renderer/scheduler/task_queue_manager.cc
index a50b6097b0b3eea97a998b5c47866a36ed14aa7b..112a37ca33c120b61319a12d587106335badfaf0 100644
--- a/content/renderer/scheduler/task_queue_manager.cc
+++ b/content/renderer/scheduler/task_queue_manager.cc
@@ -7,7 +7,6 @@
 #include <queue>
 
 #include "base/bind.h"
-#include "base/observer_list.h"
 #include "base/trace_event/trace_event.h"
 #include "base/trace_event/trace_event_argument.h"
 #include "cc/test/test_now_source.h"
@@ -414,12 +413,8 @@
     main_task_runner_->PostNonNestableTask(pending_task.posted_from,
                                            pending_task.task);
   } else {
-    FOR_EACH_OBSERVER(base::MessageLoop::TaskObserver, task_observers_,
-                      WillProcessTask(pending_task));
     task_annotator_.RunTask("TaskQueueManager::PostTask",
                             "TaskQueueManager::RunTask", pending_task);
-    FOR_EACH_OBSERVER(base::MessageLoop::TaskObserver, task_observers_,
-                      DidProcessTask(pending_task));
   }
 }
 
@@ -445,18 +440,6 @@
   DCHECK(main_thread_checker_.CalledOnValidThread());
   DCHECK_GE(work_batch_size, 1);
   work_batch_size_ = work_batch_size;
-}
-
-void TaskQueueManager::AddTaskObserver(
-    base::MessageLoop::TaskObserver* task_observer) {
-  DCHECK(main_thread_checker_.CalledOnValidThread());
-  task_observers_.AddObserver(task_observer);
-}
-
-void TaskQueueManager::RemoveTaskObserver(
-    base::MessageLoop::TaskObserver* task_observer) {
-  DCHECK(main_thread_checker_.CalledOnValidThread());
-  task_observers_.RemoveObserver(task_observer);
 }
 
 void TaskQueueManager::SetTimeSourceForTesting(