Changes instant so that the newly created tab has a new id. Doing

chrome/browser/tab_contents/navigation_controller.h

 // Copyright (c) 2010 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 CHROME_BROWSER_TAB_CONTENTS_NAVIGATION_CONTROLLER_H_
 #define CHROME_BROWSER_TAB_CONTENTS_NAVIGATION_CONTROLLER_H_
 #pragma once
 
 #include "build/build_config.h"
 
@@ skipping 346 matching lines @@
   // reload, while only a different ref would be in-page (pages can't clear
   // refs without reload, only change to "#" which we don't count as empty).
   bool IsURLInPageNavigation(const GURL& url) const;
 
   // Copies the navigation state from the given controller to this one. This
   // one should be empty (just created).
   void CopyStateFrom(const NavigationController& source);
 
   // A variant of CopyStateFrom. Removes all entries from this except the last
   // entry, inserts all entries from |source| before and including the active
-  // entry and resets the |session_id_| of this to match |source|.  This is
-  // intended for use when you're going to throw away |source| and replace it
-  // with this. This method is intended for use when the last entry of |this|
-  // is the active entry. For example:
+  // entry. This method is intended for use when the last entry of |this| is the
+  // active entry. For example:
   // source: A B *C* D
   // this:   E F *G*   (last must be active or pending)
   // result: A B *G*
   // This ignores the transient index of the source and honors that of 'this'.
   void CopyStateFromAndPrune(NavigationController* source);
 
   // Removes all the entries except the active entry. If there is a new pending
   // navigation it is preserved.
   void PruneAllButActive();
 
@@ skipping 215 matching lines @@
   static size_t max_entry_count_;
 
   // If a repost is pending, its type (RELOAD or RELOAD_IGNORING_CACHE),
   // NO_RELOAD otherwise.
   ReloadType pending_reload_;
 
   DISALLOW_COPY_AND_ASSIGN(NavigationController);
 };
 
 #endif  // CHROME_BROWSER_TAB_CONTENTS_NAVIGATION_CONTROLLER_H_