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

third_party/WebKit/public/web/WebFrameWidget.h

Index: third_party/WebKit/public/web/WebFrameWidget.h
diff --git a/third_party/WebKit/public/web/WebFrameWidget.h b/third_party/WebKit/public/web/WebFrameWidget.h
index 06ce1f3a40a383e7e3af9ef964101a9a886f6cd7..c236dfc5b22000de0fd53b32e916a7c56a67499e 100644
--- a/third_party/WebKit/public/web/WebFrameWidget.h
+++ b/third_party/WebKit/public/web/WebFrameWidget.h
@@ -60,10 +60,13 @@ class WebFrameWidget : public WebWidget {
   // directive, so that it knows whether it needs to draw or not.
   virtual void setVisibilityState(WebPageVisibilityState visibilityState) {}
 
-  // Makes the WebFrameWidget transparent.  This is useful if you want to have
-  // some custom background rendered behind it.
-  virtual bool isTransparent() const = 0;
-  virtual void setIsTransparent(bool) = 0;
+  // Overrides the WebFrameWidget's background and base background color. You
+  // can use this to enforce a transparent background, which is useful if you
+  // want to have some custom background rendered behind the widget.
+  virtual void setBackgroundColorOverride(WebColor) = 0;
+  virtual void clearBackgroundColorOverride() = 0;
+  virtual void setBaseBackgroundColorOverride(WebColor) = 0;
+  virtual void clearBaseBackgroundColorOverride() = 0;
 
   // Sets the base color used for this WebFrameWidget's background. This is in
   // effect the default background color used for pages with no