[content] Fix background color update handling in RWHVAura.

content/public/browser/render_widget_host_view.h

 // Copyright (c) 2012 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_PUBLIC_BROWSER_RENDER_WIDGET_HOST_VIEW_H_
 #define CONTENT_PUBLIC_BROWSER_RENDER_WIDGET_HOST_VIEW_H_
 
 #include <memory>
 
 #include "base/strings/string16.h"
@@ skipping 110 matching lines @@
   // Returns true if the View's context menu is showing.
   virtual bool IsShowingContextMenu() const = 0;
 
   // Tells the View whether the context menu is showing.
   virtual void SetShowingContextMenu(bool showing) = 0;
 
   // Returns the currently selected text.
   virtual base::string16 GetSelectedText() = 0;
 
   // Subclasses should override this method to set the background color. |color|
-  // could be transparent or opaque.
+  // has to be either SK_ColorTRANSPARENT or opaque. If set to
+  // SK_ColorTRANSPARENT, the renderer's background color will be overridden to
+  // be fully transparent.
   virtual void SetBackgroundColor(SkColor color) = 0;
   // Convenience method to fill the background layer with the default color by
   // calling |SetBackgroundColor|.
   virtual SkColor background_color() = 0;
   virtual void SetBackgroundColorToDefault() = 0;
   virtual bool GetBackgroundOpaque() = 0;
 
   // Return value indicates whether the mouse is locked successfully or not.
   virtual bool LockMouse() = 0;
   virtual void UnlockMouse() = 0;
@@ skipping 50 matching lines @@
   // Returns |true| if text is currently being spoken by Mac OS X.
   virtual bool IsSpeaking() const = 0;
   // Stops speaking, if it is currently in progress.
   virtual void StopSpeaking() = 0;
 #endif  // defined(OS_MACOSX)
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_RENDER_WIDGET_HOST_VIEW_H_