MD Downloads: fix double click bug

ui/webui/resources/js/action_link.js

 // 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.
 
 // Action links are elements that are used to perform an in-page navigation or
 // action (e.g. showing a dialog).
 //
 // They look like normal anchor (<a>) tags as their text color is blue. However,
 // they're subtly different as they're not initially underlined (giving users a
 // clue that underlined links navigate while action links don't).
@@ skipping 26 matching lines @@
 
     /** @this {ActionLink} */
     createdCallback: function() {
       // Action links can start disabled (e.g. <a is="action-link" disabled>).
       this.tabIndex = this.disabled ? -1 : 0;
 
       if (!this.hasAttribute('role'))
         this.setAttribute('role', 'link');
 
       this.addEventListener('keydown', function(e) {
-        if (!this.disabled && e.keyIdentifier == 'Enter') {
+        if (!this.disabled && e.keyIdentifier == 'Enter' && !this.href) {
           // Schedule a click asynchronously because other 'keydown' handlers
           // may still run later (e.g. document.addEventListener('keydown')).
           // Specifically options dialogs break when this timeout isn't here.
           // NOTE: this affects the "trusted" state of the ensuing click. I
           // haven't found anything that breaks because of this (yet).
           window.setTimeout(this.click.bind(this), 0);
         }
       });
 
       function preventDefault(e) {
@@ skipping 46 matching lines @@
     removeAttribute: function(attr) {
       if (attr.toLowerCase() == 'disabled')
         this.disabled = false;
       else
         HTMLAnchorElement.prototype.removeAttribute.apply(this, arguments);
     },
   },
 
   extends: 'a',
 });