Fix regression with back-button not working on prerendered and instant pages.

content/browser/tab_contents/tab_contents.h

 // Copyright (c) 2011 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_TAB_CONTENTS_TAB_CONTENTS_H_
 #define CONTENT_BROWSER_TAB_CONTENTS_TAB_CONTENTS_H_
 #pragma once
 
 #include <deque>
 #include <map>
@@ skipping 605 matching lines @@
   // or the dedicated set title message. It returns true if the new title is
   // different and was therefore updated.
   bool UpdateTitleForEntry(NavigationEntry* entry, const string16& title);
 
   // Causes the TabContents to navigate in the right renderer to |entry|, which
   // must be already part of the entries in the navigation controller.
   // This does not change the NavigationController state.
   bool NavigateToEntry(const NavigationEntry& entry,
                        NavigationController::ReloadType reload_type);
 
+  // Sets the history for this tab_contents to |history_length| entries, and

[Charlie Reis, 2011/08/09 20:59:31]

Sounds odd to me to "set the history for a TabContents."  History is maintained
in the NavigationController and not here, but NavigationController is the one
telling us to do this.

Perhaps we should say that it updates the history length in the current
RenderView.

[Charlie Reis, 2011/08/09 23:25:16]

Can you squeeze in this fix as well?

+  // moves the current page_id to the last entry in the list if it's valid.
+  // This is mainly used when a prerendered page is swapped into the current
+  // tab.
+  void SetHistoryLengthAndClear(int history_length);
+
+
   // Misc non-view stuff -------------------------------------------------------
 
   // Helper functions for sending notifications.
   void NotifySwapped();
   void NotifyConnected();
   void NotifyDisconnected();
 
   // RenderViewHostDelegate ----------------------------------------------------
 
   // RenderViewHostDelegate implementation.
@@ skipping 222 matching lines @@
   ObserverList<TabContentsObserver> observers_;
 
   // Content restrictions, used to disable print/copy etc based on content's
   // (full-page plugins for now only) permissions.
   int content_restrictions_;
 
   DISALLOW_COPY_AND_ASSIGN(TabContents);
 };
 
 #endif  // CONTENT_BROWSER_TAB_CONTENTS_TAB_CONTENTS_H_