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

third_party/WebKit/Source/web/WebViewFrameWidget.h

 // Copyright 2015 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 WebViewFrameWidget_h
 #define WebViewFrameWidget_h
 
 #include "platform/heap/Handle.h"
 #include "web/WebFrameWidgetBase.h"
 #include "web/WebInputMethodControllerImpl.h"
@@ skipping 65 matching lines @@
   bool isWebView() const override { return false; }
   bool isPagePopup() const override { return false; }
   void willCloseLayerTreeView() override;
   WebColor backgroundColor() const override;
   WebPagePopup* pagePopup() const override;
   bool getCompositionCharacterBounds(WebVector<WebRect>& bounds) override;
   void updateBrowserControlsState(WebBrowserControlsState constraints,
                                   WebBrowserControlsState current,
                                   bool animate) override;
   void setVisibilityState(WebPageVisibilityState) override;
-  bool isTransparent() const override;
-  void setIsTransparent(bool) override;
+  void setBackgroundColorOverride(WebColor) override;
+  void clearBackgroundColorOverride() override;
+  void setBaseBackgroundColorOverride(WebColor) override;
+  void clearBaseBackgroundColorOverride() override;
   void setBaseBackgroundColor(WebColor) override;
   WebLocalFrameImpl* localRoot() const override;
   WebInputMethodControllerImpl* getActiveWebInputMethodController()
       const override;
 
   // WebFrameWidgetBase overrides:
   bool forSubframe() const override { return false; }
   void scheduleAnimation() override;
   CompositorWorkerProxyClient* createCompositorWorkerProxyClient() override;
   AnimationWorkletProxyClient* createAnimationWorkletProxyClient() override;
   void setRootGraphicsLayer(GraphicsLayer*) override;
   void setRootLayer(WebLayer*) override;
   WebLayerTreeView* getLayerTreeView() const override;
   CompositorAnimationHost* animationHost() const override;
   WebWidgetClient* client() const override { return m_client; }
   HitTestResult coreHitTestResultAt(const WebPoint&) override;
 
  private:
   WebWidgetClient* m_client;
   RefPtr<WebViewImpl> m_webView;
   Persistent<WebLocalFrameImpl> m_mainFrame;
 };
 
 }  // namespace blink
 
 #endif  // WebViewFrameWidget_h