Use const ref for LocalFrame::LocalFrameRoot and FrameTree::Top

third_party/WebKit/Source/core/frame/Deprecation.cpp

 // Copyright 2016 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 "core/frame/Deprecation.h"
 
 #include "core/dom/Document.h"
 #include "core/dom/ExecutionContext.h"
 #include "core/frame/FrameConsole.h"
 #include "core/frame/LocalFrame.h"
@@ skipping 143 matching lines @@
                                    UseCounter::Feature feature) {
   Deprecation::CountDeprecation(document.GetFrame(), feature);
 }
 
 void Deprecation::CountDeprecationCrossOriginIframe(
     const LocalFrame* frame,
     UseCounter::Feature feature) {
   // Check to see if the frame can script into the top level document.
   SecurityOrigin* security_origin =
       frame->GetSecurityContext()->GetSecurityOrigin();
-  Frame* top = frame->Tree().Top();
-  if (top && !security_origin->CanAccess(
-                 top->GetSecurityContext()->GetSecurityOrigin()))
+  Frame& top = frame->Tree().Top();
+  if (!security_origin->CanAccess(
+          top.GetSecurityContext()->GetSecurityOrigin()))
     CountDeprecation(frame, feature);
 }
 
 void Deprecation::CountDeprecationCrossOriginIframe(
     const Document& document,
     UseCounter::Feature feature) {
   LocalFrame* frame = document.GetFrame();
   if (!frame)
     return;
   CountDeprecationCrossOriginIframe(frame, feature);
@@ skipping 237 matching lines @@
       return willBeRemoved("SVGPathElement.getPathSegAtLength", M62,
                            "5638783282184192");
 
     // Features that aren't deprecated don't have a deprecation message.
     default:
       return String();
   }
 }
 
 }  // namespace blink