Adds NavigationManager util functions to ios/chrome/browser/web/

ios/web/navigation/navigation_manager_impl.h

Index: ios/web/navigation/navigation_manager_impl.h
diff --git a/ios/web/navigation/navigation_manager_impl.h b/ios/web/navigation/navigation_manager_impl.h
index 56bd2474ff177974ba041a0bf3f0cc03601c5297..077849a439996514c6b0c5b049470edae14ca936 100644
--- a/ios/web/navigation/navigation_manager_impl.h
+++ b/ios/web/navigation/navigation_manager_impl.h
@@ -106,12 +106,6 @@ class NavigationManagerImpl : public NavigationManager {
                       ui::PageTransition navigation_type,
                       NavigationInitiationType initiation_type);
 
-  // Convenience accessors to get the underlying NavigationItems from the
-  // SessionEntries returned from |session_controller_|'s -lastUserEntry and
-  // -previousEntry methods.
-  // TODO(crbug.com/546365): Remove these methods.
-  NavigationItem* GetLastUserItem() const;
-
   // Temporary method. Returns a vector of NavigationItems corresponding to
   // the SessionEntries of the uderlying CRWSessionController.
   // TODO(crbug.com/546365): Remove this method.