Add JavaScript prompts support to CWVUIDelegate.

ios/web_view/public/cwv_ui_delegate.h

 // Copyright 2017 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.
 
 #ifndef IOS_WEB_VIEW_PUBLIC_CWV_UI_DELEGATE_H_
 #define IOS_WEB_VIEW_PUBLIC_CWV_UI_DELEGATE_H_
 
 #import <CoreGraphics/CoreGraphics.h>
 #import <UIKit/UIKit.h>
 
 @class CWVHTMLElement;
 @class CWVWebView;
 
 // UI delegate interface for a CWVWebView.  Embedders can implement the
 // functions in order to customize library behavior.
 @protocol CWVUIDelegate<NSObject>
 
 @optional
 // Instructs the delegate to present context menu in response to user’s long
 // press gesture at |location| in |view| coordinate space. |element| is an HTML
 // element which received the gesture.
 - (void)webView:(CWVWebView*)webView
     runContextMenuWithTitle:(NSString*)menuTitle
              forHTMLElement:(CWVHTMLElement*)element
                      inView:(UIView*)view
         userGestureLocation:(CGPoint)location;
 
+// Instructs the delegate to show UI in response to window.alert JavaScript
+// call.
+- (void)webView:(CWVWebView*)webView
+    runJavaScriptAlertPanelWithMessage:(NSString*)message
+                               pageURL:(NSURL*)URL
+                     completionHandler:(void (^)(void))completionHandler;
+
+// Instructs the delegate to show UI in response to window.confirm JavaScript
+// call.
+- (void)webView:(CWVWebView*)webView
+    runJavaScriptConfirmPanelWithMessage:(NSString*)message
+                                 pageURL:(NSURL*)URL
+                       completionHandler:(void (^)(BOOL))completionHandler;
+
+// Instructs the delegate to show UI in response to window.prompt JavaScript
+// call.
+- (void)webView:(CWVWebView*)webView
+    runJavaScriptTextInputPanelWithPrompt:(NSString*)prompt
+                              defaultText:(NSString*)defaultText
+                                  pageURL:(NSURL*)URL
+                        completionHandler:
+                            (void (^)(NSString*))completionHandler;
+
 @end
 
 #endif  // IOS_WEB_VIEW_PUBLIC_CWV_UI_DELEGATE_H_