Fix popunders spawned from a subframe.

content/browser/frame_host/frame_tree_node.h

 // Copyright 2013 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.
 
 #ifndef CONTENT_BROWSER_FRAME_HOST_FRAME_TREE_NODE_H_
 #define CONTENT_BROWSER_FRAME_HOST_FRAME_TREE_NODE_H_
 
 #include <stddef.h>
 
 #include <memory>
@@ skipping 105 matching lines @@
 
   FrameTreeNode* original_opener() const { return original_opener_; }
 
   // Assigns a new opener for this node and, if |opener| is non-null, registers
   // an observer that will clear this node's opener if |opener| is ever
   // destroyed.
   void SetOpener(FrameTreeNode* opener);
 
   // Assigns the initial opener for this node, and if |opener| is non-null,
   // registers an observer that will clear this node's opener if |opener| is
-  // ever destroyed.
+  // ever destroyed. The value set here is the root of the tree.
+  //
   // It is not possible to change the opener once it was set.
   void SetOriginalOpener(FrameTreeNode* opener);
 
   FrameTreeNode* child_at(size_t index) const {
     return children_[index].get();
   }
 
   // Returns the URL of the last committed page in the current frame.
   const GURL& current_url() const {
     return current_frame_host()->last_committed_url();
@@ skipping 266 matching lines @@
   // browser process activities to this node (when possible).  It is unrelated
   // to the core logic of FrameTreeNode.
   FrameTreeNodeBlameContext blame_context_;
 
   DISALLOW_COPY_AND_ASSIGN(FrameTreeNode);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_FRAME_HOST_FRAME_TREE_NODE_H_