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

content/renderer/render_frame_impl.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_RENDERER_RENDER_FRAME_IMPL_H_
 #define CONTENT_RENDERER_RENDER_FRAME_IMPL_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 415 matching lines @@
   bool OnMessageReceived(const IPC::Message& msg) override;
   void OnAssociatedInterfaceRequest(
       const std::string& interface_name,
       mojo::ScopedInterfaceEndpointHandle handle) override;
 
   // RenderFrame implementation:
   RenderView* GetRenderView() override;
   RenderAccessibility* GetRenderAccessibility() override;
   int GetRoutingID() override;
   blink::WebLocalFrame* GetWebFrame() override;
-  WebPreferences& GetWebkitPreferences() override;
+  const WebPreferences& GetWebkitPreferences() override;
   int ShowContextMenu(ContextMenuClient* client,
                       const ContextMenuParams& params) override;
   void CancelContextMenu(int request_id) override;
   blink::WebPlugin* CreatePlugin(
       blink::WebFrame* frame,
       const WebPluginInfo& info,
       const blink::WebPluginParams& params,
       std::unique_ptr<PluginInstanceThrottler> throttler) override;
   void LoadURLExternally(const blink::WebURLRequest& request,
                          blink::WebNavigationPolicy policy) override;
@@ skipping 1002 matching lines @@
   struct PendingNavigationInfo {
     blink::WebNavigationType navigation_type;
     blink::WebNavigationPolicy policy;
     bool replaces_current_history_item;
     bool history_navigation_in_new_child_frame;
     bool client_redirect;
     bool cache_disabled;
     blink::WebFormElement form;
     blink::WebSourceLocation source_location;
 
-    PendingNavigationInfo(const NavigationPolicyInfo& info);
+    explicit PendingNavigationInfo(const NavigationPolicyInfo& info);
   };
 
   // PlzNavigate: Contains information about a pending navigation to be sent to
   // the browser. This state is allocated in decidePolicyForNavigation() and
   // is used and released in didStartProvisionalLoad().
   std::unique_ptr<PendingNavigationInfo> pending_navigation_info_;
 
   service_manager::BindSourceInfo browser_info_;
 
   mojo::BindingSet<service_manager::mojom::InterfaceProvider>
       interface_provider_bindings_;
 
   mojom::URLLoaderFactoryPtr url_loader_factory_;
 
   // AndroidOverlay routing token from the browser, if we have one yet.
   base::Optional<base::UnguessableToken> overlay_routing_token_;
 
   // Callbacks that we should call when we get a routing token.
   std::vector<media::RoutingTokenCallback> pending_routing_token_callbacks_;
 
   base::WeakPtrFactory<RenderFrameImpl> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderFrameImpl);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_RENDER_FRAME_IMPL_H_