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

third_party/WebKit/Source/core/dom/IntersectionObservation.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/dom/IntersectionObservation.h"
 
 #include "core/dom/ElementRareData.h"
 #include "core/dom/IntersectionObserver.h"
 #include "core/frame/LocalFrame.h"
 #include "core/layout/IntersectionGeometry.h"
@@ skipping 83 matching lines @@
 
 void IntersectionObservation::UpdateShouldReportRootBoundsAfterDomChange() {
   if (!Observer()->RootIsImplicit()) {
     should_report_root_bounds_ = true;
     return;
   }
   should_report_root_bounds_ = false;
   LocalFrame* target_frame = Target()->GetDocument().GetFrame();
   if (!target_frame)
     return;
-  Frame* root_frame = target_frame->Tree().Top();
-  DCHECK(root_frame);
-  if (root_frame == target_frame) {
+  Frame& root_frame = target_frame->Tree().Top();
+  if (&root_frame == target_frame) {
     should_report_root_bounds_ = true;
   } else {
     should_report_root_bounds_ =
         target_frame->GetSecurityContext()->GetSecurityOrigin()->CanAccess(
-            root_frame->GetSecurityContext()->GetSecurityOrigin());
+            root_frame.GetSecurityContext()->GetSecurityOrigin());
   }
 }
 
 DEFINE_TRACE(IntersectionObservation) {
   visitor->Trace(observer_);
   visitor->Trace(target_);
 }
 
 }  // namespace blink