[MD History] Add shift-selection to the history lists.

chrome/browser/resources/md_history/history_toolbar.js

 // Copyright 2015 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.
 
 Polymer({
   is: 'history-toolbar',
   properties: {
     // Number of history items currently selected.
-    // TODO(calamity): bind this to
-    // listContainer.selectedItem.selectedPaths.length.

[tsergeant, 2016/08/15 04:49:50]

This is still relevant, right? There are still cases where it would be nice not
to fire an 'unselect-all' just in case the toolbar needs to be reset.

[calamity, 2016/08/15 07:18:40]

Hmm. Ok, restored. I'm not convinced there's a nice way to bind this actually...

     count: {
       type: Number,
       value: 0,
       observer: 'changeToolbarView_'
     },
 
     // True if 1 or more history items are selected. When this value changes
     // the background colour changes.
     itemsSelected_: {
       type: Boolean,
@@ skipping 109 matching lines @@
     // TODO(calamity): Fix the format of these dates.
     return loadTimeData.getStringF(
       'historyInterval', queryStartTime, queryEndTime);
   },
 
   /** @private */
   hasDrawerChanged_: function() {
     this.updateStyles();
   },
 });