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

third_party/WebKit/Source/core/page/ChromeClient.h

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple, Inc. All rights
  * reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).
  * Copyright (C) 2012 Samsung Electronics. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 351 matching lines @@
                                                     bool is_reload) = 0;
   virtual bool OpenJavaScriptAlertDelegate(LocalFrame*, const String&) = 0;
   virtual bool OpenJavaScriptConfirmDelegate(LocalFrame*, const String&) = 0;
   virtual bool OpenJavaScriptPromptDelegate(LocalFrame*,
                                             const String& message,
                                             const String& default_value,
                                             String& result) = 0;
   virtual void PrintDelegate(LocalFrame*) = 0;
 
  private:
-  bool CanOpenModalIfDuringPageDismissal(Frame* main_frame,
+  bool CanOpenModalIfDuringPageDismissal(Frame& main_frame,
                                          DialogType,
                                          const String& message);
   void SetToolTip(LocalFrame&, const HitTestResult&);
 
   WeakMember<Node> last_mouse_over_node_;
   LayoutPoint last_tool_tip_point_;
   String last_tool_tip_text_;
 
   FRIEND_TEST_ALL_PREFIXES(ChromeClientTest, SetToolTipFlood);
 };
 
 }  // namespace blink
 
 #endif  // ChromeClient_h