Only handle click actions for left & middle buttons

ui/webui/resources/js/util.js

 // Copyright (c) 2012 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.
 
 // <include src="assert.js">
 
 /**
  * Alias for document.getElementById. Found elements must be HTMLElements.
  * @param {string} id The ID of the element to find.
  * @return {HTMLElement} The found element or null if not found.
@@ skipping 196 matching lines @@
 function queryRequiredElement(selectors, opt_context) {
   var element = (opt_context || document).querySelector(selectors);
   return assertInstanceof(element, HTMLElement,
                           'Missing required element: ' + selectors);
 }
 
 // Handle click on a link. If the link points to a chrome: or file: url, then
 // call into the browser to do the navigation.
 ['click', 'auxclick'].forEach(function(eventName) {
   document.addEventListener(eventName, function(e) {
+    if (e.button > 1)
+      return; // Ignore buttons other than left and middle.
     if (e.defaultPrevented)
       return;
 
     var eventPath = e.path;
     var anchor = null;
     if (eventPath) {
       for (var i = 0; i < eventPath.length; i++) {
         var element = eventPath[i];
         if (element.tagName === 'A' && element.href) {
           anchor = element;
@@ skipping 250 matching lines @@
         case 0xdb: return '[';
         case 0xdd: return ']';
       }
       return 'Unidentified';
     }
   });
 } else {
   window.console.log("KeyboardEvent.Key polyfill not required");
 }
 // </if>  /* is_ios */