Sets a transparent background for out-of-process subframes.

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 37 matching lines @@
     // away from WebView inheriting WebWidget.
     // TODO(dcheng): Remove once transition is complete.
     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, bool isInitialState) { }
 
+    // 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;
+
+    // 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;
+
     // TODO(dcheng): Temporary: there should only be one WebFrameWidget
     // implementation but the Blink API is currently in a transition state.
     // See https://goo.gl/7yVrnb. These methods should only be used inside
     // blink.
     virtual bool forSubframe() const { return true; }
     virtual void scheduleAnimation() = 0;
 };
 
 } // namespace blink
 
 #endif