FrameTree::Find only searches relative to local frames.

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 131 matching lines @@
 
 unsigned FrameTree::ChildCount() const {
   unsigned count = 0;
   for (Frame* result = FirstChild(); result;
        result = result->Tree().NextSibling())
     ++count;
   return count;
 }
 
 Frame* FrameTree::Find(const AtomicString& name) const {
+  // Named frame lookup should always be relative to a local frame.
+  DCHECK(this_frame_->IsLocalFrame());
+
   if (EqualIgnoringASCIICase(name, "_self") ||
       EqualIgnoringASCIICase(name, "_current") || name.IsEmpty())
     return this_frame_;
 
   if (EqualIgnoringASCIICase(name, "_top"))
     return &Top();
 
   if (EqualIgnoringASCIICase(name, "_parent"))
     return Parent() ? Parent() : this_frame_.Get();
 
@@ skipping 134 matching lines @@
 void showFrameTree(const blink::Frame* frame) {
   if (!frame) {
     printf("Null input frame\n");
     return;
   }
 
   printFrames(&frame->Tree().Top(), frame, 0);
 }
 
 #endif