Fix DirectCompositionSurfaceTest.TestMakeCurrent flakiness.

gpu/ipc/service/child_window_win.h

 // Copyright 2017 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.
 
 #ifndef GPU_IPC_SERVICE_CHILD_WINDOW_WIN_H_
 #define GPU_IPC_SERVICE_CHILD_WINDOW_WIN_H_
 
 #include "base/memory/weak_ptr.h"
+#include "base/task_runner.h"
 #include "gpu/ipc/service/image_transport_surface_delegate.h"
 
 #include <windows.h>
 
 namespace gpu {
 
 struct SharedData;
 
 // The window DirectComposition renders into needs to be owned by the process
 // that's currently doing the rendering. The class creates and owns a window
 // which is reparented by the browser to be a child of its window.
 class ChildWindowWin {
  public:
   ChildWindowWin(base::WeakPtr<ImageTransportSurfaceDelegate> delegate,
                  HWND parent_window);
   ~ChildWindowWin();
 
   bool Initialize();
   void ClearInvalidContents();
   HWND window() const { return window_; }
 
+  scoped_refptr<base::TaskRunner> GetTaskRunnerForTesting();
+
  private:
   // This member contains all the data that can be accessed from the main or
   // window owner threads.
   std::unique_ptr<SharedData> shared_data_;
   // The eventual parent of the window living in the browser process.
   HWND parent_window_;
   HWND window_;
   // The window is initially created with this parent window. We need to keep it
   // around so that we can destroy it at the end.
   HWND initial_parent_window_;
   base::WeakPtr<ImageTransportSurfaceDelegate> delegate_;
 
   DISALLOW_COPY_AND_ASSIGN(ChildWindowWin);
 };
 
 }  // namespace gpu
 
 #endif  // GPU_IPC_SERVICE_CHILD_WINDOW_WIN_H_