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

third_party/WebKit/Source/core/dom/IntersectionObservation.cpp

Index: third_party/WebKit/Source/core/dom/IntersectionObservation.cpp
diff --git a/third_party/WebKit/Source/core/dom/IntersectionObservation.cpp b/third_party/WebKit/Source/core/dom/IntersectionObservation.cpp
index 0c79d878eaccee27d0bf512e2d9d0469d0973d5a..ed53ec8ea51bb5ba569e7d9dbad0362095c28d81 100644
--- a/third_party/WebKit/Source/core/dom/IntersectionObservation.cpp
+++ b/third_party/WebKit/Source/core/dom/IntersectionObservation.cpp
@@ -101,14 +101,13 @@ void IntersectionObservation::UpdateShouldReportRootBoundsAfterDomChange() {
   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());
   }
 }