Always create FrameTreeNodes and RenderFrameHosts for every frame.

content/browser/frame_host/frame_tree_node.cc

 // 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.
 
 #include "content/browser/frame_host/frame_tree_node.h"
 
 #include <queue>
 
 #include "base/stl_util.h"
 #include "content/browser/frame_host/navigator.h"
@@ skipping 38 matching lines @@
     if ((*iter) == child)
       break;
   }
 
   if (iter != children_.end())
     children_.erase(iter);
 }
 
 void FrameTreeNode::ResetForMainFrame(
     RenderFrameHostImpl* new_render_frame_host) {
-  DCHECK_EQ(0UL, children_.size());
-
   owns_render_frame_host_ = false;
   frame_id_ = kInvalidFrameId;
   current_url_ = GURL();
+
+  // The children may not have been cleared if a cross-process navigation
+  // commits before the old process cleans everything up.  Make sure the child
+  // nodes get deleted.
   children_.clear();
 
   render_frame_host_ = new_render_frame_host;
 }
 
 }  // namespace content