Returning early when setting a frame name to the same name.

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

 /*
  * Copyright (C) 2006, 2007, 2008, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 1038 matching lines @@
         return nullAtom;
 
     return frame()->tree().name();
 }
 
 void LocalDOMWindow::setName(const AtomicString& name)
 {
     if (!isCurrentlyDisplayedInFrame())
         return;
 
+    if (name == frame()->tree().name())
+        return;
+
     frame()->tree().setName(name);
     ASSERT(frame()->loader().client());
     frame()->loader().client()->didChangeName(name, frame()->tree().uniqueName());

[dcheng, 2016/06/15 11:18:35]

I'd suggest moving this into FrameTree::setName() so we don't have to duplicate
the check.

[Łukasz Anforowicz, 2016/06/15 17:46:22]

I think this is a great idea.  At the same time, I'd like to do this in a
separate CL.

I was guessing that some calls to FrameTree::setName would not propagate back to
the browser - moving the FrameLoaderClient notification to FrameTree::setName
should plug this hole.  OTOH, this probably needs some tests to show that there
actually is a problem (and therefore I'd like to do this in a separate CL). 
FWIW, I couldn't repro this problem yet (I thought that the setName call in
createNewWindow would not be propagated).

I also need to note that moving client notification can result in unnecessary
notifications in cases when 1) the browser already knows the new name, but 2)
FrameTree name has not been setup yet.  For such cases:

- We should still have correct, same behavior (because such unnecessary IPCs
should be ignored by FrameTreeNode::SetFrameName (after seeing new_name ==
old_name).

- In the long-term such cases should go through FrameTree::setPrecalculatedName
instead of FrameTree::setName (but this is tricky because the format is only
exposed through Blink's "core" layer, not through "web" layer).

 }
 
 void LocalDOMWindow::setStatus(const String& string)
 {
     m_status = string;
 
     if (!frame())
         return;
 
     FrameHost* host = frame()->host();
@@ skipping 478 matching lines @@
 {
     // If the LocalDOMWindow still has a frame reference, that frame must point
     // back to this LocalDOMWindow: otherwise, it's easy to get into a situation
     // where script execution leaks between different LocalDOMWindows.
     if (m_frameObserver->frame())
         ASSERT_WITH_SECURITY_IMPLICATION(m_frameObserver->frame()->domWindow() == this);
     return m_frameObserver->frame();
 }
 
 } // namespace blink