[MediaRouter] Update MR-2-Extension's PostMessage to return boolean.

chrome/browser/media/router/mock_media_router.h

Index: chrome/browser/media/router/mock_media_router.h
diff --git a/chrome/browser/media/router/mock_media_router.h b/chrome/browser/media/router/mock_media_router.h
index c093a0e99cb87cab904bc0825e2fdd8aa51fe79f..61c71a308055065062be66dc0020d083578f2242 100644
--- a/chrome/browser/media/router/mock_media_router.h
+++ b/chrome/browser/media/router/mock_media_router.h
@@ -28,9 +28,10 @@ class MockMediaRouter : public MediaRouter {
                     const MediaSink::Id& sink_id,
                     const MediaRouteResponseCallback& callback));
   MOCK_METHOD1(CloseRoute, void(const MediaRoute::Id& route_id));
-  MOCK_METHOD2(PostMessage,
+  MOCK_METHOD3(PostMessage,
                void(const MediaRoute::Id& route_id,
-                    const std::string& message));
+                    const std::string& message,
+                    const PostMessageCallback& callback));
   MOCK_METHOD1(ClearIssue, void(const Issue::Id& issue_id));
   MOCK_METHOD1(AddIssuesObserver, void(IssuesObserver* observer));
   MOCK_METHOD1(RemoveIssuesObserver, void(IssuesObserver* observer));