Ensure that unique ids are unique.

content/browser/frame_host/navigation_entry_impl.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/navigation_entry_impl.h"
 
 #include <queue>
 
 #include "base/metrics/histogram.h"
 #include "base/strings/string_util.h"
@@ skipping 323 matching lines @@
   extra_data_.erase(key);
 }
 
 NavigationEntryImpl* NavigationEntryImpl::Clone() const {
   NavigationEntryImpl* copy = new NavigationEntryImpl();
 
   // TODO(creis): Only share the same FrameNavigationEntries if cloning within
   // the same tab.
   copy->frame_tree_.reset(frame_tree_->Clone());
 
-  // Copy all state over, unless cleared in ResetForCommit.
-  copy->unique_id_ = unique_id_;
+  // Copy most state over, unless cleared in ResetForCommit.
+  // Don't copy unique_id_, otherwise it won't be unique.
   copy->bindings_ = bindings_;
   copy->page_type_ = page_type_;
   copy->virtual_url_ = virtual_url_;
   copy->update_virtual_url_with_url_ = update_virtual_url_with_url_;
   copy->title_ = title_;
   copy->favicon_ = favicon_;
   copy->page_state_ = page_state_;
   copy->page_id_ = page_id_;
   copy->ssl_ = ssl_;
   copy->transition_type_ = transition_type_;
@@ skipping 167 matching lines @@
   screenshot_ = png_data;
   if (screenshot_.get())
     UMA_HISTOGRAM_MEMORY_KB("Overscroll.ScreenshotSize", screenshot_->size());
 }
 
 GURL NavigationEntryImpl::GetHistoryURLForDataURL() const {
   return GetBaseURLForDataURL().is_empty() ? GURL() : GetVirtualURL();
 }
 
 }  // namespace content