Fix history page middle click action

chrome/browser/resources/synthetic_middleclick.js

 // Copyright 2016 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.
 
 (function() {
 
 var middleButtonMouseDownTarget = null;
 
 document.addEventListener('mousedown', function(e) {
   if (e.button == 1)
     middleButtonMouseDownTarget = e.path[0];
 }, true);
 
 document.addEventListener('mouseup', function(e) {
   if (e.button != 1)
     return;
 
   if (e.path.length > 0 && e.path[0] == middleButtonMouseDownTarget)
     middleButtonMouseDownTarget.dispatchEvent(new MouseEvent('click', e));
 
   middleButtonMouseDownTarget = null;
 }, true);
 
+// Prevent the synthetic click to open a new tab as the new tab will
+// open if the click happened on a link regardless of this synthetic
+// event.

[Dan Beam, 2016/05/31 21:34:32]

i don't understand what this comment means.  can you try again?

[Navid Zolghadr, 2016/06/01 18:46:16]

How about this?

+window.addEventListener('click', function(e) {
+  if (e.button == 1 && !e.isTrusted)

[Dan Beam, 2016/05/31 21:34:32]

don't we control the code that's doing this?  why not just do:

if (e.path.length > 0 && e.path[0] == middleButtonMouseDownTarget) {
  var click = new MouseEvent('click', e);
  middleButtonMouseDownTarget.dispatchEvent(click);
  click.preventDefault();
}

[Navid Zolghadr, 2016/06/01 18:46:16]

Maybe the new comment explains this a little better. Basically when js
dispatches the click event the default handlers will run right after all the
handlers. So basically your proposal doesn't prevent the default behavior of the
click event as the new tab is already opened right before the
click.preventDefault() line. So I need to preventDefault it in a handler (that
runs the last preferably). The other solution is to prevent defaulting it before
dispatching it but that causes some unexpected behavior in the current code as
the handlers we have here ignores the events if they were preventDefaulted
already.

+    e.preventDefault();
+});
+
 })();