[Navigation Experiment] Add WKBasedNavigationManagerImpl.

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 92f7fbb9def3a5cb967d6c3d28eb7c669b060769..31a5f3e44ef1883d947e7efa678289064cf4cd18 100644
--- a/ios/web/navigation/navigation_manager_impl.h
+++ b/ios/web/navigation/navigation_manager_impl.h
@@ -132,11 +132,19 @@ class NavigationManagerImpl : public NavigationManager {
   // NavigationManagerImpl.
   friend SessionStorageBuilder;
 
+  // TODO(crbug.com/738020): Remove legacy code and merge
+  // WKBasedNavigationManager into this class after the navigation experiment.
+
   // Identical to GetItemAtIndex() but returns the underlying NavigationItemImpl
   // instead of the public NavigationItem interface. This is used by
   // SessionStorageBuilder to persist session state.
   virtual NavigationItemImpl* GetNavigationItemImplAtIndex(
       size_t index) const = 0;
+
+  // Checks whether or not two URL are an in-page navigation (differing only
+  // in the fragment).
+  static bool AreUrlsFragmentChangeNavigation(const GURL& existing_url,
+                                              const GURL& new_url);
 };
 
 }  // namespace web