Remove windows/mac/ios specific code from //ui

ui/gl/gl_fence_apple.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 UI_GL_GL_FENCE_APPLE_H_
-#define UI_GL_GL_FENCE_APPLE_H_
-
-#include "base/macros.h"
-#include "ui/gl/gl_bindings.h"
-#include "ui/gl/gl_fence.h"
-
-namespace gfx {
-
-class GL_EXPORT GLFenceAPPLE : public GLFence {
- public:
-  GLFenceAPPLE();
-  ~GLFenceAPPLE() override;
-
-  // GLFence implementation:
-  bool HasCompleted() override;
-  void ClientWait() override;
-  void ServerWait() override;
-
- private:
-  GLuint fence_;
-
-  DISALLOW_COPY_AND_ASSIGN(GLFenceAPPLE);
-};
-
-}  // namespace gfx
-
-#endif  // UI_GL_GL_FENCE_APPLE_H_