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);
+
+// If js sends a synthetic click event to an element like what we do
+// here the default handler runs for that event. Now if user middle
+// clicks on an element Chrome by default runs the default behavior
+// (i.e. opening the link in a new tab) with firing no click event.
+// See crbug.com/255. This file does send that synthetic click for
+// middle click to temporary fix the expected behavours in some
+// click handlers. However, this will cause yet another tab to open
+// if the target is a link as the default handler runs for this synthetic
+// as well if the event is not prevented.

[Dan Beam, 2016/06/02 19:18:33]

yeah, sorry, this still doesn't make much sense to me.

probably just remove it

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