Replace more ObserverList with base::ObserverList.

ui/events/platform/platform_event_source.cc

Index: ui/events/platform/platform_event_source.cc
diff --git a/ui/events/platform/platform_event_source.cc b/ui/events/platform/platform_event_source.cc
index bf957f07476f590f917e017280e3a0b8cfcd4880..99f69ac37390acd646819bbe8f5c8b1427bf2b71 100644
--- a/ui/events/platform/platform_event_source.cc
+++ b/ui/events/platform/platform_event_source.cc
@@ -76,7 +76,7 @@ uint32_t PlatformEventSource::DispatchEvent(PlatformEvent platform_event) {
 
   if ((action & POST_DISPATCH_PERFORM_DEFAULT) &&
       dispatchers_.might_have_observers()) {
-    ObserverList<PlatformEventDispatcher>::Iterator iter(&dispatchers_);
+    base::ObserverList<PlatformEventDispatcher>::Iterator iter(&dispatchers_);
     while (PlatformEventDispatcher* dispatcher = iter.GetNext()) {
       if (dispatcher->CanDispatchEvent(platform_event))
         action = dispatcher->DispatchEvent(platform_event);