Revert of Attempting to resolve a race condition with PowerMonitor

content/browser/renderer_host/media/media_stream_manager.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/renderer_host/media/media_stream_manager.h"
 
 #include <list>
 #include <vector>
 
 #include "base/bind.h"
@@ skipping 343 matching lines @@
   // initialization is done synchronously.
   if (BrowserThread::CurrentlyOn(BrowserThread::IO)) {
     InitializeDeviceManagersOnIOThread();
   } else {
     BrowserThread::PostTask(
         BrowserThread::IO, FROM_HERE,
         base::Bind(&MediaStreamManager::InitializeDeviceManagersOnIOThread,
                    base::Unretained(this)));
   }
 
-  base::PowerMonitor::AddObserver(this);
+  base::PowerMonitor* power_monitor = base::PowerMonitor::Get();
+  // BrowserMainLoop always creates the PowerMonitor instance before creating
+  // MediaStreamManager, but power_monitor may be NULL in unit tests.
+  if (power_monitor)
+    power_monitor->AddObserver(this);
 }
 
 MediaStreamManager::~MediaStreamManager() {
   DVLOG(1) << "~MediaStreamManager";
   DCHECK(requests_.empty());
   DCHECK(!device_task_runner_);
 
-  base::PowerMonitor::RemoveObserver(this);
+  base::PowerMonitor* power_monitor = base::PowerMonitor::Get();
+  // The PowerMonitor instance owned by BrowserMainLoops always outlives the
+  // MediaStreamManager, but it may be NULL in unit tests.
+  if (power_monitor)
+    power_monitor->RemoveObserver(this);
 }
 
 VideoCaptureManager* MediaStreamManager::video_capture_manager() {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   DCHECK(video_capture_manager_.get());
   return video_capture_manager_.get();
 }
 
 AudioInputDeviceManager* MediaStreamManager::audio_input_device_manager() {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
@@ skipping 1529 matching lines @@
       if (it->device.type == MEDIA_DESKTOP_VIDEO_CAPTURE) {
         video_capture_manager_->SetDesktopCaptureWindowId(it->session_id,
                                                           window_id);
         break;
       }
     }
   }
 }
 
 }  // namespace content