Revert of Attempting to resolve a race condition with PowerMonitor

content/browser/renderer_host/media/media_stream_manager.cc

Index: content/browser/renderer_host/media/media_stream_manager.cc
diff --git a/content/browser/renderer_host/media/media_stream_manager.cc b/content/browser/renderer_host/media/media_stream_manager.cc
index ea0d546b193f3d7f0eb3cb86db3a4fd03c449a05..af543fc26d562756c7c3a4a2aa2e42cfd572ab9f 100644
--- a/content/browser/renderer_host/media/media_stream_manager.cc
+++ b/content/browser/renderer_host/media/media_stream_manager.cc
@@ -361,7 +361,11 @@
                    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() {
@@ -369,7 +373,11 @@
   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() {