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

ios/web/navigation/crw_session_controller.h

Index: ios/web/navigation/crw_session_controller.h
diff --git a/ios/web/navigation/crw_session_controller.h b/ios/web/navigation/crw_session_controller.h
index 3e6b98a1edf1649af7029e26d7419729b4fe325e..50adc7a020e55cf4d18b8f37b5a837f6a19d72ac 100644
--- a/ios/web/navigation/crw_session_controller.h
+++ b/ios/web/navigation/crw_session_controller.h
@@ -114,6 +114,7 @@ struct SSLStatus;
 // 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;
@@ -154,6 +155,11 @@ struct SSLStatus;
 // 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_