Fix thread-safety of PushMessagingMessageFilter

content/browser/push_messaging/push_messaging_message_filter.h

Index: content/browser/push_messaging/push_messaging_message_filter.h
diff --git a/content/browser/push_messaging/push_messaging_message_filter.h b/content/browser/push_messaging/push_messaging_message_filter.h
index f9812704783d08628ebf4637bbca0d98f7105514..752c6ca361c8087f567e152030b56c2cbdac16f6 100644
--- a/content/browser/push_messaging/push_messaging_message_filter.h
+++ b/content/browser/push_messaging/push_messaging_message_filter.h
@@ -87,7 +87,10 @@ class PushMessagingMessageFilter : public BrowserMessageFilter {
   // Owned by the content embedder's browsing context.
   PushMessagingService* service_;
 
-  base::WeakPtrFactory<PushMessagingMessageFilter> weak_factory_;
+  // Should only be used for asynchronous calls to the PushMessagingService on
+  // the UI thread, which may have external dependencies that supersede the
+  // lifetime of this messaging filter.
+  base::WeakPtrFactory<PushMessagingMessageFilter> weak_factory_ui_to_ui_;
 
   DISALLOW_COPY_AND_ASSIGN(PushMessagingMessageFilter);
 };