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

content/renderer/render_frame_impl.cc

 // 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.
 
 #include "content/renderer/render_frame_impl.h"
 
 #include <map>
 #include <string>
 #include <utility>
 #include <vector>
@@ skipping 2469 matching lines @@
 
 int RenderFrameImpl::GetRoutingID() {
   return routing_id_;
 }
 
 blink::WebLocalFrame* RenderFrameImpl::GetWebFrame() {
   DCHECK(frame_);
   return frame_;
 }
 
-WebPreferences& RenderFrameImpl::GetWebkitPreferences() {
+const WebPreferences& RenderFrameImpl::GetWebkitPreferences() {
   return render_view_->GetWebkitPreferences();
 }
 
 int RenderFrameImpl::ShowContextMenu(ContextMenuClient* client,
                                      const ContextMenuParams& params) {
   DCHECK(client);  // A null client means "internal" when we issue callbacks.
   ContextMenuParams our_params(params);
 
   blink::WebRect position_in_window(params.x, params.y, 0, 0);
   GetRenderWidget()->ConvertViewportToWindow(&position_in_window);
@@ skipping 4595 matching lines @@
       policy(info.default_policy),
       replaces_current_history_item(info.replaces_current_history_item),
       history_navigation_in_new_child_frame(
           info.is_history_navigation_in_new_child_frame),
       client_redirect(info.is_client_redirect),
       cache_disabled(info.is_cache_disabled),
       form(info.form),
       source_location(info.source_location) {}
 
 }  // namespace content