[ios] Removed canGoBack/canGoForward API from CRWSessionController.

ios/web/public/navigation_manager.h

 // 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.
 
 #ifndef IOS_WEB_PUBLIC_NAVIGATION_MANAGER_H_
 #define IOS_WEB_PUBLIC_NAVIGATION_MANAGER_H_
 
 #include <stddef.h>
 
 #import "base/mac/scoped_nsobject.h"
@@ skipping 118 matching lines @@
   virtual int GetPendingItemIndex() const = 0;
 
   // Removes the item at the specified |index|.  If the index is the last
   // committed index or the pending item, this does nothing and returns false.
   // Otherwise this call discards any transient or pending entries.
   virtual bool RemoveItemAtIndex(int index) = 0;
 
   // Navigation relative to the current item.
   virtual bool CanGoBack() const = 0;
   virtual bool CanGoForward() const = 0;
+  virtual bool CanGoToOffset(int offset) const = 0;
   virtual void GoBack() = 0;
   virtual void GoForward() = 0;
 
   // Navigates to the specified absolute index.
   virtual void GoToIndex(int index) = 0;
 
   // Reloads the current entry. If |check_for_repost| is true and the current
   // entry has POST data the user is prompted to see if they really want to
   // reload the page. In nearly all cases pass in true.  If a transient entry
   // is showing, initiates a new navigation to its URL.
   virtual void Reload(bool check_for_repost) = 0;
 };
 
 }  // namespace web
 
 #endif  // IOS_WEB_PUBLIC_NAVIGATION_MANAGER_H_