Add ShellDelegate, MediaDelegate and KeyboardUI stubs to mus ash

ash/gpu_support_stub.h

-// Copyright 2014 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 ASH_GPU_SUPPORT_STUB_H_
-#define ASH_GPU_SUPPORT_STUB_H_
-
-#include "ash/ash_export.h"
-#include "ash/gpu_support.h"
-#include "base/compiler_specific.h"
-#include "base/macros.h"
-
-namespace ash {
-
-// A GPUSupport object that does not depend on src/content.
-class ASH_EXPORT GPUSupportStub : public GPUSupport {
- public:
-  GPUSupportStub();
-  ~GPUSupportStub() override;
-
- private:
-  // Overridden from GPUSupport:
-  bool IsPanelFittingDisabled() const override;
-  void DisableGpuWatchdog() override;
-  void GetGpuProcessHandles(
-      const GetGpuProcessHandlesCallback& callback) const override;
-
-  DISALLOW_COPY_AND_ASSIGN(GPUSupportStub);
-};
-
-}  // namespace ash
-
-#endif  // ASH_GPU_SUPPORT_STUB_H_