Add CWVUIDelegate with method to customize context menu.

ios/web_view/public/cwv_html_element.h

Index: ios/web_view/public/cwv_html_element.h
diff --git a/ios/web_view/public/cwv_html_element.h b/ios/web_view/public/cwv_html_element.h
new file mode 100644
index 0000000000000000000000000000000000000000..cf7a7ea7293b640224fe1ee8244a4ef5bf555e9e
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+++ b/ios/web_view/public/cwv_html_element.h
@@ -0,0 +1,22 @@
+// 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_HTML_ELEMENT_H_
+#define IOS_WEB_VIEW_PUBLIC_CWV_HTML_ELEMENT_H_
+
+#import <Foundation/Foundation.h>
+
+// Encapsulates information about HTML element. Used in
+// delegate methods.
+@interface CWVHTMLElement : NSObject
+
+// |href| property of an HTML element.
+@property(nullable, copy, readonly) NSURL* hyperlink;
+// |src| property of an HTML element.
+@property(nullable, copy, readonly) NSURL* mediaSource;
+// |innerText| property of an HTML element.
+@property(nullable, copy, readonly) NSString* text;
+@end
+
+#endif  // IOS_WEB_VIEW_PUBLIC_CWV_HTML_ELEMENT_H_