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

content/renderer/render_view_impl.cc

 // 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.
 
 #include "content/renderer/render_view_impl.h"
 
 #include <algorithm>
 #include <cmath>
 #include <memory>
 
@@ skipping 1958 matching lines @@
 }
 
 gfx::Size RenderViewImpl::GetSize() const {
   return size();
 }
 
 float RenderViewImpl::GetDeviceScaleFactor() const {
   return device_scale_factor_;
 }
 
-WebPreferences& RenderViewImpl::GetWebkitPreferences() {
+const WebPreferences& RenderViewImpl::GetWebkitPreferences() {
   return webkit_preferences_;
 }
 
 void RenderViewImpl::SetWebkitPreferences(const WebPreferences& preferences) {
   OnUpdateWebPreferences(preferences);
 }
 
 blink::WebView* RenderViewImpl::GetWebView() {
   return webview();
 }
@@ skipping 679 matching lines @@
                         input_event.GetCoalescedEventsPointers(), latency_info,
                         dispatch_type);
     return INPUT_EVENT_ACK_STATE_NOT_CONSUMED;
   }
   idle_user_detector_->ActivityDetected();
   return RenderWidget::HandleInputEvent(input_event, latency_info,
                                         dispatch_type);
 }
 
 }  // namespace content