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

base/message_pump_android.cc

Index: base/message_pump_android.cc
diff --git a/base/message_pump_android.cc b/base/message_pump_android.cc
index 2daf98db3157fa8ac9aed43ce34052745119836b..456e49ad954f3dac5d8525fcbc26bf43106df485 100644
--- a/base/message_pump_android.cc
+++ b/base/message_pump_android.cc
@@ -61,7 +61,7 @@ static jboolean DoRunLoopOnce(JNIEnv* env, jobject obj, jint native_delegate) {
 namespace base {
 
 MessagePumpForUI::MessagePumpForUI()
-    : state_(NULL) {
+    : run_loop_(NULL) {
 }
 
 MessagePumpForUI::~MessagePumpForUI() {
@@ -73,7 +73,8 @@ void MessagePumpForUI::Run(Delegate* delegate) {
 }
 
 void MessagePumpForUI::Start(Delegate* delegate) {
-  state_ = new MessageLoop::AutoRunState(MessageLoop::current());
+  run_loop_ = new MessageLoop::RunLoop();
+  run_loop_->BeforeRun();
 
   DCHECK(g_system_message_handler_obj.Get().is_null());
 
@@ -94,9 +95,10 @@ void MessagePumpForUI::Quit() {
     g_system_message_handler_obj.Get().Reset();
   }
 
-  if (state_) {
-    delete state_;
-    state_ = NULL;
+  if (run_loop_) {
+    run_loop_->AfterRun();
+    delete run_loop_;
+    run_loop_ = NULL;
   }
 }