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

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

 // Copyright 2014 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/DOMWindow.h"
 
 #include <memory>
 
 #include "bindings/core/v8/WindowProxyManager.h"
 #include "core/dom/Document.h"
@@ skipping 88 matching lines @@
     return nullptr;
 
   Frame* parent = GetFrame()->Tree().Parent();
   return parent ? parent->DomWindow() : GetFrame()->DomWindow();
 }
 
 DOMWindow* DOMWindow::top() const {
   if (!GetFrame())
     return nullptr;
 
-  return GetFrame()->Tree().Top()->DomWindow();
+  return GetFrame()->Tree().Top().DomWindow();
 }
 
 DOMWindow* DOMWindow::AnonymousIndexedGetter(uint32_t index) const {
   if (!GetFrame())
     return nullptr;
 
   Frame* child = GetFrame()->Tree().ScopedChild(index);
   return child ? child->DomWindow() : nullptr;
 }
 
@@ skipping 101 matching lines @@
                                            ->GetSecurityOrigin()
                                            ->ToString());
   if (MixedContentChecker::IsMixedContent(source_document->GetSecurityOrigin(),
                                           target_url)) {
     UseCounter::Count(GetFrame(), UseCounter::kPostMessageFromSecureToInsecure);
   } else if (MixedContentChecker::IsMixedContent(
                  GetFrame()->GetSecurityContext()->GetSecurityOrigin(),
                  source_document->Url())) {
     UseCounter::Count(GetFrame(), UseCounter::kPostMessageFromInsecureToSecure);
     if (MixedContentChecker::IsMixedContent(
-            GetFrame()->Tree().Top()->GetSecurityContext()->GetSecurityOrigin(),
+            GetFrame()->Tree().Top().GetSecurityContext()->GetSecurityOrigin(),
             source_document->Url())) {
       UseCounter::Count(GetFrame(),
                         UseCounter::kPostMessageFromInsecureToSecureToplevel);
     }
   }
 
   MessageEvent* event =
       MessageEvent::Create(std::move(channels), std::move(message),
                            source_origin, String(), source, source_suborigin);
 
@@ skipping 205 matching lines @@
   visitor->Trace(location_);
   EventTargetWithInlineData::Trace(visitor);
 }
 
 DEFINE_TRACE_WRAPPERS(DOMWindow) {
   visitor->TraceWrappers(location_);
   EventTargetWithInlineData::TraceWrappers(visitor);
 }
 
 }  // namespace blink