[Navigation Experiment] Add WKBasedNavigationManagerImpl.

ios/web/web_state/web_state_impl.h

Index: ios/web/web_state/web_state_impl.h
diff --git a/ios/web/web_state/web_state_impl.h b/ios/web/web_state/web_state_impl.h
index fbdb248beebc4e5b0d214cf3389329c59ee6519d..bdd308912d34d702d1485464b08205716ee17c08 100644
--- a/ios/web/web_state/web_state_impl.h
+++ b/ios/web/web_state/web_state_impl.h
@@ -19,6 +19,7 @@
 #include "base/values.h"
 #import "ios/web/navigation/navigation_manager_delegate.h"
 #import "ios/web/navigation/navigation_manager_impl.h"
+#import "ios/web/navigation/web_view_navigation_proxy_impl.h"
 #import "ios/web/public/java_script_dialog_callback.h"
 #include "ios/web/public/java_script_dialog_type.h"
 #import "ios/web/public/web_state/web_state.h"
@@ -48,6 +49,7 @@ class WebInterstitialImpl;
 class WebStateInterfaceProvider;
 class WebStatePolicyDecider;
 class WebUIIOS;
+class WebViewNavigationProxy;
 
 // Implementation of WebState.
 // Generally mirrors //content's WebContents implementation.
@@ -269,6 +271,7 @@ class WebStateImpl : public WebState, public NavigationManagerDelegate {
   void UpdateHttpResponseHeaders(const GURL& url);
 
   WebState* GetWebState() override;
+  WebViewNavigationProxy* GetWebViewNavigationProxy() const override;
 
  protected:
   void AddObserver(WebStateObserver* observer) override;