Move a bunch of content\common code into the content namespace.

content/renderer/active_notification_tracker.h

Index: content/renderer/active_notification_tracker.h
===================================================================
--- content/renderer/active_notification_tracker.h	(revision 163359)
+++ content/renderer/active_notification_tracker.h	(working copy)
@@ -17,6 +17,8 @@
 class WebNotificationPermissionCallback;
 }
 
+namespace content {
+
 // This class manages the set of active Notification objects in either
 // a render or worker process.  This class should be accessed only on
 // the main thread.
@@ -55,4 +57,6 @@
   DISALLOW_COPY_AND_ASSIGN(ActiveNotificationTracker);
 };
 
+}  // namespace content
+
 #endif  // CONTENT_RENDERER_ACTIVE_NOTIFICATION_TRACKER_H_