Add NavigationEntryImpl::TreeNode for tracking FrameNavigationEntries.

content/browser/frame_host/frame_navigation_entry.cc

 // Copyright 2015 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_navigation_entry.h"
 
 namespace content {
 
 FrameNavigationEntry::FrameNavigationEntry() {
 }
 
 FrameNavigationEntry::FrameNavigationEntry(SiteInstanceImpl* site_instance,
                                            const GURL& url,
                                            const Referrer& referrer)
     : site_instance_(site_instance), url_(url), referrer_(referrer) {
 }
 
 FrameNavigationEntry::~FrameNavigationEntry() {
 }
 
+FrameNavigationEntry* FrameNavigationEntry::Clone() const {
+  FrameNavigationEntry* copy = new FrameNavigationEntry();
+
+  copy->site_instance_ = site_instance_;
+  copy->url_ = url_;
+  copy->referrer_ = referrer_;
+
+  return copy;
+}
+
 }  // namespace content