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

ash/drag_drop/drag_drop_controller.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/drag_drop/drag_drop_controller.h"
 
 #include "ash/drag_drop/drag_image_view.h"
 #include "ash/shell.h"
 #include "base/message_loop.h"
+#include "base/run_loop.h"
 #include "ui/aura/client/capture_client.h"
 #include "ui/aura/client/drag_drop_delegate.h"
 #include "ui/aura/cursor_manager.h"
 #include "ui/aura/env.h"
 #include "ui/aura/root_window.h"
 #include "ui/aura/window.h"
 #include "ui/base/dragdrop/drag_drop_types.h"
 #include "ui/base/dragdrop/os_exchange_data_provider_aura.h"
 #include "ui/compositor/layer.h"
 #include "ui/compositor/layer_animator.h"
@@ skipping 55 matching lines @@
   drag_image_->SetScreenBounds(gfx::Rect(
         root_location.Subtract(drag_image_offset_),
         drag_image_->GetPreferredSize()));
   drag_image_->SetWidgetVisible(true);
 
   drag_window_ = NULL;
   drag_start_location_ = root_location.Subtract(drag_image_offset_);
 
 #if !defined(OS_MACOSX)
   if (should_block_during_drag_drop_) {
+    base::RunLoop run_loop(aura::Env::GetInstance()->GetDispatcher());
+    quit_closure_ = run_loop.QuitClosure();
     MessageLoopForUI* loop = MessageLoopForUI::current();
     MessageLoop::ScopedNestableTaskAllower allow_nested(loop);
-    loop->RunWithDispatcher(aura::Env::GetInstance()->GetDispatcher());
+    run_loop.Run();
   }
 #endif  // !defined(OS_MACOSX)
 
   return drag_operation_;
 }
 
 void DragDropController::DragUpdate(aura::Window* target,
                                     const aura::LocatedEvent& event) {
   aura::client::DragDropDelegate* delegate = NULL;
   if (target != drag_window_) {
@@ skipping 58 matching lines @@
     if (drag_operation_ == 0)
       StartCanceledAnimation();
     else
       drag_image_.reset();
   } else {
     drag_image_.reset();
   }
 
   Cleanup();
   if (should_block_during_drag_drop_)
-    MessageLoop::current()->QuitNow();
+    quit_closure_.Run();
 }
 
 void DragDropController::DragCancel() {
   aura::Env::GetInstance()->cursor_manager()->SetCursor(ui::kCursorPointer);
 
   // |drag_window_| can be NULL if we have just started the drag and have not
   // received any DragUpdates, or, if the |drag_window_| gets destroyed during
   // a drag/drop.
   aura::client::DragDropDelegate* delegate = drag_window_?
       aura::client::GetDragDropDelegate(drag_window_) : NULL;
   if (delegate)
     delegate->OnDragExited();
 
   Cleanup();
   drag_operation_ = 0;
   StartCanceledAnimation();
   if (should_block_during_drag_drop_)
-    MessageLoop::current()->QuitNow();
+    quit_closure_.Run();
 }
 
 bool DragDropController::IsDragDropInProgress() {
   return drag_drop_in_progress_;
 }
 
 bool DragDropController::PreHandleKeyEvent(aura::Window* target,
                                            aura::KeyEvent* event) {
   return false;
 }
@@ skipping 83 matching lines @@
 void DragDropController::Cleanup() {
   if (drag_window_)
     drag_window_->RemoveObserver(this);
   drag_window_ = NULL;
   drag_data_ = NULL;
   drag_drop_in_progress_ = false;
 }
 
 }  // namespace internal
 }  // namespace ash