Update ios/web_view/shell UIDelegate implementation.

ios/web_view/internal/cwv_web_view.mm

Index: ios/web_view/internal/cwv_web_view.mm
diff --git a/ios/web_view/internal/cwv_web_view.mm b/ios/web_view/internal/cwv_web_view.mm
index 08fb97d0cad8000af7e293c22ba15bca521b574e..44574ef2a297964588ed65bcad3e05d74a6f6be3 100644
--- a/ios/web_view/internal/cwv_web_view.mm
+++ b/ios/web_view/internal/cwv_web_view.mm
@@ -79,6 +79,10 @@
         base::MakeUnique<ios_web_view::WebViewWebStatePolicyDecider>(
             _webState.get(), self);
 
+    _javaScriptDialogPresenter =
+        base::MakeUnique<ios_web_view::WebViewJavaScriptDialogPresenter>(
+            self, nullptr);
+
     // Initialize Translate.
     ios_web_view::WebViewTranslateClient::CreateForWebState(_webState.get());
   }