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

content/renderer/render_view_impl.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_RENDERER_RENDER_VIEW_IMPL_H_
 #define CONTENT_RENDERER_RENDER_VIEW_IMPL_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 334 matching lines @@
   virtual void didScrollWithKeyboard(const blink::WebSize& delta);
 #endif
 
   // RenderView implementation -------------------------------------------------
 
   bool Send(IPC::Message* message) override;
   RenderFrameImpl* GetMainRenderFrame() override;
   int GetRoutingID() const override;
   gfx::Size GetSize() const override;
   float GetDeviceScaleFactor() const override;
-  WebPreferences& GetWebkitPreferences() override;
+  const WebPreferences& GetWebkitPreferences() override;
   void SetWebkitPreferences(const WebPreferences& preferences) override;
   blink::WebView* GetWebView() override;
   blink::WebFrameWidget* GetWebFrameWidget() override;
   bool ShouldDisplayScrollbars(int width, int height) const override;
   bool GetContentStateImmediately() const override;
   void Repaint(const gfx::Size& size) override;
   void SetEditCommandForNextKeyEvent(const std::string& name,
                                      const std::string& value) override;
   void ClearEditCommands() override;
   const std::string& GetAcceptLanguages() const override;
@@ skipping 463 matching lines @@
   // ---------------------------------------------------------------------------
 
   base::WeakPtrFactory<RenderViewImpl> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderViewImpl);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_RENDER_VIEW_IMPL_H_