Reland: [ios] Refactored back-forward navigation in CRWSessionController.

ios/web/navigation/crw_session_controller.h

 // Copyright 2012 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_NAVIGATION_CRW_SESSION_CONTROLLER_H_
 #define IOS_WEB_NAVIGATION_CRW_SESSION_CONTROLLER_H_
 
 #import <Foundation/Foundation.h>
 #include <vector>
 
@@ skipping 96 matching lines @@
 // Copies history state from the given CRWSessionController and adds it to this
 // controller. If |replaceState|, replaces the state of this controller with
 // the state of |otherSession|, instead of appending.
 - (void)copyStateFromAndPrune:(CRWSessionController*)otherSession
                  replaceState:(BOOL)replaceState;
 
 // Returns YES if there are entries to go back or forward to, given the
 // current entry.
 - (BOOL)canGoBack;
 - (BOOL)canGoForward;
+- (BOOL)canGoDelta:(int)delta;
 // Adjusts the current entry to reflect the navigation in the corresponding
 // direction in history.
 - (void)goBack;
 - (void)goForward;
 // Calls goBack or goForward the appropriate number of times to adjust
 // currentNavigationIndex_ by delta.
 - (void)goDelta:(int)delta;
 // Sets |currentNavigationIndex_| to the index of |entry| if |entries_| contains
 // |entry|.
 - (void)goToEntry:(CRWSessionEntry*)entry;
@@ skipping 20 matching lines @@
                                     andEntry:(CRWSessionEntry*)secondEntry;
 
 // Find the most recent session entry that is not a redirect. Returns nil if
 // |entries_| is empty.
 - (CRWSessionEntry*)lastUserEntry;
 
 // Set |useDesktopUserAgentForNextPendingEntry_| to YES if there is no pending
 // entry, otherwise set |useDesktopUserAgent| in the pending entry.
 - (void)useDesktopUserAgentForNextPendingEntry;
 
+// Returns the navigation index that differs from the current entry by the
+// specified |delta|, skipping redirect navigation items. The index returned is
+// not guaranteed to be valid.
+- (NSInteger)indexOfEntryForDelta:(int)delta;
+
 @end
 
 #endif  // IOS_WEB_NAVIGATION_CRW_SESSION_CONTROLLER_H_