Mark Render{Frame,View}::GetWebkitPreferences() return values as const.

content/public/renderer/render_frame.h

 // Copyright 2013 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_RENDERER_RENDER_FRAME_H_
 #define CONTENT_PUBLIC_RENDERER_RENDER_FRAME_H_
 
 #include <stddef.h>
 
 #include <memory>
@@ skipping 97 matching lines @@
   // Return the RenderAccessibility associated with this frame.
   virtual RenderAccessibility* GetRenderAccessibility() = 0;
 
   // Get the routing ID of the frame.
   virtual int GetRoutingID() = 0;
 
   // Returns the associated WebFrame.
   virtual blink::WebLocalFrame* GetWebFrame() = 0;
 
   // Gets WebKit related preferences associated with this frame.
-  virtual WebPreferences& GetWebkitPreferences() = 0;
+  virtual const WebPreferences& GetWebkitPreferences() = 0;
 
   // Shows a context menu with the given information. The given client will
   // be called with the result.
   //
   // The request ID will be returned by this function. This is passed to the
   // client functions for identification.
   //
   // If the client is destroyed, CancelContextMenu() should be called with the
   // request ID returned by this function.
   //
   // Note: if you end up having clients outliving the RenderFrame, we should add
   // a CancelContextMenuCallback function that takes a request id.
   virtual int ShowContextMenu(ContextMenuClient* client,
                               const ContextMenuParams& params) = 0;
 
   // Cancels a context menu in the event that the client is destroyed before the
   // menu is closed.
   virtual void CancelContextMenu(int request_id) = 0;
 
-  // Create a new NPAPI/Pepper plugin depending on |info|. Returns NULL if no
-  // plugin was found. |throttler| may be empty.
+  // Create a new Pepper plugin depending on |info|. Returns NULL if no plugin
+  // was found. |throttler| may be empty.
   virtual blink::WebPlugin* CreatePlugin(
       blink::WebFrame* frame,
       const WebPluginInfo& info,
       const blink::WebPluginParams& params,
       std::unique_ptr<PluginInstanceThrottler> throttler) = 0;
 
   // The client should handle the navigation externally.
   virtual void LoadURLExternally(const blink::WebURLRequest& request,
                                  blink::WebNavigationPolicy policy) = 0;
 
@@ skipping 117 matching lines @@
 
  private:
   // This interface should only be implemented inside content.
   friend class RenderFrameImpl;
   RenderFrame() {}
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_RENDERER_RENDER_FRAME_H_