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

third_party/WebKit/Source/core/page/FrameTree.cpp

 /*
  * Copyright (C) Research In Motion Limited 2010. All rights reserved.
  * Copyright (C) 2006 Apple Computer, Inc.
  *
  * 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.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 36 matching lines @@
     , m_scopedChildCount(invalidChildCount)
 {
 }
 
 FrameTree::~FrameTree()
 {
 }
 
 void FrameTree::setName(const AtomicString& name)
 {
+    // Do not recalculate m_uniqueName if there is no real change of m_name.
+    // This is not just a performance optimization - other code relies on the
+    // assumption that unique name shouldn't change if the assigned name didn't
+    // change (i.e. code in content::FrameTreeNode::SetFrameName).
+    if (m_name == name) {
+        // Assert that returning early below won't leave m_uniqueName in an
+        // uninitialized state - it should only be null if m_name is also
+        // null and only if it is for the main frame.
+        // m_uniqueName.isNull() should imply m_name.isNull() && !parent().
+        // this FrameTree is for a main frame.
+        DCHECK(!m_uniqueName.isNull() || (m_name.isNull() && !parent()));
+        return;
+    }
+
     m_name = name;
 
     // Remove our old frame name so it's not considered in calculateUniqueNameForChildFrame
     // and appendUniqueSuffix calls below.
     m_uniqueName = AtomicString();
 
     // Calculate a new unique name based on inputs.
     if (parent()) {
         setUniqueName(
             parent()->tree().calculateUniqueNameForChildFrame(m_thisFrame, name, nullAtom));
@@ skipping 510 matching lines @@
 {
     if (!frame) {
         printf("Null input frame\n");
         return;
     }
 
     printFrames(frame->tree().top(), frame, 0);
 }
 
 #endif