DNS: Testing for [blink] Support (semi-)transparent background colors.

third_party/WebKit/public/web/WebFrameWidget.h

 /*
  * Copyright (C) 2014 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 42 matching lines @@
   BLINK_EXPORT static WebFrameWidget* create(WebWidgetClient*,
                                              WebView*,
                                              WebLocalFrame* mainFrame);
 
   // Sets the visibility of the WebFrameWidget.
   // We still track page-level visibility, but additionally we need to notify a
   // WebFrameWidget when its owning RenderWidget receives a Show or Hide
   // 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
   // background-color style in effect, or used as the alpha-blended basis for
   // any pages with translucent background-color style. (For pages with opaque
   // background-color style, this property is effectively ignored).
   // Setting this takes effect for the currently loaded page, if any, and
   // persists across subsequent navigations. Defaults to white prior to the
   // first call to this method.
   virtual void setBaseBackgroundColor(WebColor) = 0;
@@ skipping 42 matching lines @@
 
   // Constrains the viewport intersection for use by IntersectionObserver.
   // This is needed for out-of-process iframes to know if they are clipped
   // by ancestor frames in another process.
   virtual void setRemoteViewportIntersection(const WebRect&) {}
 };
 
 }  // namespace blink
 
 #endif