[blink] Support (semi-)transparent background colors in WebView/Frame.

content/renderer/gpu/render_widget_compositor.h

 // Copyright (c) 2013 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 CONTENT_RENDERER_GPU_RENDER_WIDGET_COMPOSITOR_H_
 #define CONTENT_RENDERER_GPU_RENDER_WIDGET_COMPOSITOR_H_
 
 #include <stdint.h>
 
 #include "base/callback.h"
@@ skipping 109 matching lines @@
   cc::FrameSinkId getFrameSinkId() override;
   void setRootLayer(const blink::WebLayer& layer) override;
   void clearRootLayer() override;
   cc::AnimationHost* compositorAnimationHost() override;
   void setViewportSize(const blink::WebSize& device_viewport_size) override;
   blink::WebSize getViewportSize() const override;
   virtual blink::WebFloatPoint adjustEventPointForPinchZoom(
       const blink::WebFloatPoint& point) const;
   void setDeviceScaleFactor(float device_scale) override;
   void setBackgroundColor(blink::WebColor color) override;
-  void setHasTransparentBackground(bool transparent) override;
   void setVisible(bool visible) override;
   void setPageScaleFactorAndLimits(float page_scale_factor,
                                    float minimum,
                                    float maximum) override;
   void startPageScaleAnimation(const blink::WebPoint& destination,
                                bool use_anchor,
                                float new_page_scale,
                                double duration_sec) override;
   bool hasPendingPageScaleAnimation() const override;
   void heuristicsForGpuRasterizationUpdated(bool matches_heuristics) override;
@@ skipping 99 matching lines @@
   blink::WebLayoutAndPaintAsyncCallback* layout_and_paint_async_callback_;
 
   cc::FrameSinkId frame_sink_id_;
 
   base::WeakPtrFactory<RenderWidgetCompositor> weak_factory_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_GPU_RENDER_WIDGET_COMPOSITOR_H_