Replace more ObserverList with base::ObserverList.

ui/events/platform/platform_event_source.h

Index: ui/events/platform/platform_event_source.h
diff --git a/ui/events/platform/platform_event_source.h b/ui/events/platform/platform_event_source.h
index 009476c6b7a818f0bfaa8f9cd010fb3fd7b09f1e..a20fe6b8e5c34cce79fb118237499a91f8a57a89 100644
--- a/ui/events/platform/platform_event_source.h
+++ b/ui/events/platform/platform_event_source.h
@@ -81,10 +81,12 @@ class EVENTS_EXPORT PlatformEventSource {
 
   void OnOverriddenDispatcherRestored();
 
-  // Use an ObserverList<> instead of an std::vector<> to store the list of
+  // Use an 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_;
 
@@ -92,7 +94,7 @@ class EVENTS_EXPORT PlatformEventSource {
   // 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);
 };