Add base::RunLoop and update ui_test_utils to use it to reduce flakiness

ash/wm/toplevel_window_event_filter.h

Index: ash/wm/toplevel_window_event_filter.h
diff --git a/ash/wm/toplevel_window_event_filter.h b/ash/wm/toplevel_window_event_filter.h
index 7f0915e4cb0bf0fd986b256acc108c1740cf2368..377ae38aeda03064f172e0bb2df8c6b4f2eac780 100644
--- a/ash/wm/toplevel_window_event_filter.h
+++ b/ash/wm/toplevel_window_event_filter.h
@@ -8,6 +8,7 @@
 
 #include <set>
 
+#include "base/callback.h"
 #include "base/compiler_specific.h"
 #include "base/memory/scoped_ptr.h"
 #include "ui/aura/client/window_move_client.h"
@@ -92,6 +93,8 @@ class ASH_EXPORT ToplevelWindowEventFilter :
 
   scoped_ptr<WindowResizer> window_resizer_;
 
+  base::Closure quit_closure_;
+
   DISALLOW_COPY_AND_ASSIGN(ToplevelWindowEventFilter);
 };