Update from https://crrev.com/333737

ui/events/platform/platform_event_source.h

 // Copyright 2014 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.
 
 #ifndef UI_EVENTS_PLATFORM_PLATFORM_EVENT_SOURCE_H_
 #define UI_EVENTS_PLATFORM_PLATFORM_EVENT_SOURCE_H_
 
 #include <map>
 #include <vector>
 
@@ skipping 63 matching lines @@
   // stream of events and wait until the next iteration of the message-loop to
   // dispatch the rest of the events.
   virtual void StopCurrentEventStream();
 
   // This is invoked when the list of dispatchers changes (i.e. a new dispatcher
   // is added, or a dispatcher is removed).
   virtual void OnDispatcherListChanged();
 
   void OnOverriddenDispatcherRestored();
 
-  // Use an ObserverList<> instead of an std::vector<> to store the list of
+  // Use a base::ObserverList<> instead of an std::vector<> to store the list of
   // dispatchers, so that adding/removing dispatchers during an event dispatch
   // is well-defined.
-  typedef ObserverList<PlatformEventDispatcher> PlatformEventDispatcherList;
+  typedef base::ObserverList<PlatformEventDispatcher>
+      PlatformEventDispatcherList;
   PlatformEventDispatcherList dispatchers_;
   PlatformEventDispatcher* overridden_dispatcher_;
 
   // Used to keep track of whether the current override-dispatcher has been
   // reset and a previous override-dispatcher has been restored.
   bool overridden_dispatcher_restored_;
 
-  ObserverList<PlatformEventObserver> observers_;
+  base::ObserverList<PlatformEventObserver> observers_;
 
   DISALLOW_COPY_AND_ASSIGN(PlatformEventSource);
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_PLATFORM_PLATFORM_EVENT_SOURCE_H_