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

content/renderer/render_frame_impl.h

Index: content/renderer/render_frame_impl.h
diff --git a/content/renderer/render_frame_impl.h b/content/renderer/render_frame_impl.h
index 1fdeefe8b219d6f7c70b82c170e2078dfea06117..8568b97df1dfc5d3ae3edeade50bf99fe43c6987 100644
--- a/content/renderer/render_frame_impl.h
+++ b/content/renderer/render_frame_impl.h
@@ -433,7 +433,7 @@ class CONTENT_EXPORT RenderFrameImpl
   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;
@@ -1456,7 +1456,7 @@ class CONTENT_EXPORT RenderFrameImpl
     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