Remove background obscuration checks.

sky/engine/core/rendering/RenderLayerModelObject.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2006, 2007, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2010, 2012 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 39 matching lines @@
     bool hasSelfPaintingLayer() const;
     RenderLayer* layer() const { return m_layer.get(); }
     ScrollableArea* scrollableArea() const;
 
     virtual void styleWillChange(StyleDifference, const RenderStyle& newStyle) override;
     virtual void styleDidChange(StyleDifference, const RenderStyle* oldStyle) override;
     virtual void updateFromStyle() { }
 
     virtual LayerType layerTypeRequired() const = 0;
 
-    // Returns true if the background is painted opaque in the given rect.
-    // The query rect is given in local coordinate system.
-    virtual bool backgroundIsKnownToBeOpaqueInRect(const LayoutRect&) const { return false; }
-
     // This is null for anonymous renderers.
     ContainerNode* node() const { return toContainerNode(RenderObject::node()); }
 protected:
     void createLayer(LayerType);
 
     virtual void willBeDestroyed() override;
 private:
     virtual bool isLayerModelObject() const override final { return true; }
 
     OwnPtr<RenderLayer> m_layer;
 
     // Used to store state between styleWillChange and styleDidChange
     static bool s_wasFloating;
 };
 
 DEFINE_RENDER_OBJECT_TYPE_CASTS(RenderLayerModelObject, isLayerModelObject());
 
 } // namespace blink
 
 #endif  // SKY_ENGINE_CORE_RENDERING_RENDERLAYERMODELOBJECT_H_