Add missing IDL definition of referrerPolicy attribute to <link>

third_party/WebKit/Source/core/html/HTMLLinkElement.idl

 /*
  * Copyright (C) 2006, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Samuel Weinig <sam.weinig@gmail.com>
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 15 matching lines @@
     // https://www.w3.org/Bugs/Public/show_bug.cgi?id=14703
     [Reflect, Measure] attribute boolean disabled;
     [Reflect, URL] attribute DOMString href;
     [CEReactions, Reflect, ReflectOnly=("anonymous","use-credentials"), ReflectEmpty="anonymous", ReflectInvalid="anonymous"] attribute DOMString? crossOrigin;
     [CEReactions, Reflect] attribute DOMString rel;
     [CEReactions, PutForwards=value] readonly attribute DOMTokenList relList;
     [CEReactions, Reflect] attribute DOMString media;
     [CEReactions, Reflect] attribute DOMString hreflang;
     [CEReactions, Reflect] attribute DOMString type;
     [Reflect] attribute DOMString as;
+    [CEReactions, Reflect, ReflectOnly=("","no-referrer","origin","no-referrer-when-downgrade","origin-when-cross-origin","unsafe-url"), ReflectMissing="", ReflectInvalid=""] attribute DOMString referrerPolicy;
     [CEReactions, PutForwards=value] readonly attribute DOMTokenList sizes;
 
     // obsolete members
     // https://html.spec.whatwg.org/#HTMLLinkElement-partial
     [CEReactions, Reflect] attribute DOMString charset;
     [CEReactions, Reflect] attribute DOMString rev;
     [CEReactions, Reflect] attribute DOMString target;
 
     // HTMLLinkElement implements LinkStyle
     // https://dev.w3.org/csswg/cssom/#the-linkstyle-interface
     readonly attribute StyleSheet? sheet;
 
     // HTML Imports
     // https://w3c.github.io/webcomponents/spec/imports/#interface-import
     readonly attribute Document? import;
 
     // Subresource Integrity
     // https://w3c.github.io/webappsec-subresource-integrity/#HTMLLinkElement
     [Reflect] attribute DOMString integrity;
 
     // Service workers
     // https://w3c.github.io/ServiceWorker/#link-element-interface-extensions
     [Reflect, OriginTrialEnabled=LinkServiceWorker] attribute USVString scope;
 };