views: Remove unused PaintLock API.

ui/views/paint_lock.h

-// 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.
-
-#ifndef UI_VIEWS_PAINT_LOCK_H_
-#define UI_VIEWS_PAINT_LOCK_H_
-
-#include "base/basictypes.h"
-#include "ui/views/views_export.h"
-
-namespace views {
-
-class View;
-
-// Instances of PaintLock can be created to disable painting of the view
-// (compositing is not disabled). When the class is destroyed, painting is
-// re-enabled. This can be useful during operations like animations, that are
-// sensitive to costly paints, and during which only composting, not painting,
-// is required.
-class VIEWS_EXPORT PaintLock {
- public:
-  // The paint lock does not own the view. It is an error for the view to be
-  // destroyed before the lock.
-  explicit PaintLock(View* view);
-  ~PaintLock();
-
- private:
-  View* view_;
-
-  DISALLOW_COPY_AND_ASSIGN(PaintLock);
-};
-
-} // namespace views
-
-#endif  // UI_VIEWS_PAINT_LOCK_H_