Update ios/web_view/shell UIDelegate implementation.

ios/web_view/internal/cwv_web_view.mm

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "ios/web_view/public/cwv_web_view.h"
 
 #include <memory>
 #include <utility>
 
 #import "base/ios/weak_nsobject.h"
@@ skipping 61 matching lines @@
 
     _webStateObserver =
         base::MakeUnique<web::WebStateObserverBridge>(_webState.get(), self);
     _webStateDelegate = base::MakeUnique<web::WebStateDelegateBridge>(self);
     _webState->SetDelegate(_webStateDelegate.get());
 
     _webStatePolicyDecider =
         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());
   }
   return self;
 }
 
 - (void)willMoveToSuperview:(UIView*)newSuperview {
   [super willMoveToSuperview:newSuperview];
   UIView* subview = _webState->GetView();
   if (subview.superview == self) {
@@ skipping 170 matching lines @@
     [_UIDelegate webViewDidClose:self];
   }
 }
 
 - (web::JavaScriptDialogPresenter*)javaScriptDialogPresenterForWebState:
     (web::WebState*)webState {
   return _javaScriptDialogPresenter.get();
 }
 
 @end