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

base/message_pump_android.h

Index: base/message_pump_android.h
diff --git a/base/message_pump_android.h b/base/message_pump_android.h
index 7310db67fbaa4f41478c7aa1b487ba7506e4eea9..29cf03995c87d744dc0e8ecbbf9ab20df6e383e1 100644
--- a/base/message_pump_android.h
+++ b/base/message_pump_android.h
@@ -7,11 +7,11 @@
 #pragma once
 
 #include "base/compiler_specific.h"
-#include "base/message_loop.h"
 #include "base/message_pump.h"
 #include "base/time.h"
 
 namespace base {
+class RunLoop;
 
 // This class implements a MessagePump needed for TYPE_UI MessageLoops on
 // OS_ANDROID platform.
@@ -28,7 +28,7 @@ class MessagePumpForUI : public MessagePump {
   virtual void Start(Delegate* delegate);
 
  private:
-  MessageLoop::AutoRunState* state_;
+  base::RunLoop* run_loop_;
 
   DISALLOW_COPY_AND_ASSIGN(MessagePumpForUI);
 };