[Navigation Experiment] Add WKBasedNavigationManagerImpl.

ios/web/web_state/ui/crw_web_controller.mm

Index: ios/web/web_state/ui/crw_web_controller.mm
diff --git a/ios/web/web_state/ui/crw_web_controller.mm b/ios/web/web_state/ui/crw_web_controller.mm
index 3e2f9597d079cd86685fa630f4b6f91d9a6b75d1..87e56e2c7396c72028c472cb8b23434add31937c 100644
--- a/ios/web/web_state/ui/crw_web_controller.mm
+++ b/ios/web/web_state/ui/crw_web_controller.mm
@@ -88,6 +88,7 @@
 #import "ios/web/web_state/ui/crw_swipe_recognizer_provider.h"
 #import "ios/web/web_state/ui/crw_web_controller.h"
 #import "ios/web/web_state/ui/crw_web_controller_container_view.h"
+#import "ios/web/web_state/ui/crw_web_view_navigation_proxy.h"
 #import "ios/web/web_state/ui/crw_web_view_proxy_impl.h"
 #import "ios/web/web_state/ui/crw_wk_navigation_states.h"
 #import "ios/web/web_state/ui/crw_wk_script_message_router.h"
@@ -1425,6 +1426,12 @@ const NSTimeInterval kSnapshotOverlayTransition = 0.5;
   return _webViewProxy.get();
 }
 
+- (id<CRWWebViewNavigationProxy>)webViewNavigationProxy {
+  DCHECK(
+      [self.webView conformsToProtocol:@protocol(CRWWebViewNavigationProxy)]);
+  return static_cast<id<CRWWebViewNavigationProxy>>(self.webView);
+}
+
 - (UIView*)viewForPrinting {
   // Printing is not supported for native controllers.
   return _webView;