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

chrome/browser/resources/md_history/history_item.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.
 
 cr.define('md_history', function() {
   var HistoryItem = Polymer({
     is: 'history-item',
 
     properties: {
       // Underlying HistoryEntry data for this item. Contains read-only fields
@@ skipping 19 matching lines @@
 
       numberOfItems: {type: Number},
 
       // The path of this history item inside its parent.
       path: String,
     },
 
     /**
      * When a history-item is selected the toolbar is notified and increases
      * or decreases its count of selected items accordingly.
+     * @param {MouseEvent} e
      * @private
      */
-    onCheckboxSelected_: function() {
+    onCheckboxSelected_: function(e) {
       // TODO(calamity): Fire this event whenever |selected| changes.
       this.fire('history-checkbox-select', {
         element: this,
-        countAddition: this.$.checkbox.checked ? 1 : -1
+        shiftKey: e.shiftKey,
       });
+      e.preventDefault();
     },
 
     /**
+     * @param {MouseEvent} e
+     * @private
+     */
+    onCheckboxMousedown_: function(e) {
+      // Prevent shift clicking a checkbox from selecting text.
+      if (e.shiftKey)
+        e.preventDefault();
+    },
+
+    /**
      * Remove bookmark of current item when bookmark-star is clicked.
      * @private
      */
     onRemoveBookmarkTap_: function() {
       if (!this.item.starred)
         return;
 
       if (this.$$('#bookmark-star') == this.root.activeElement)
         this.$['menu-button'].focus();
 
@@ skipping 76 matching lines @@
 
     if (searchedTerm)
       return currentItem.dateShort != nextItem.dateShort;
 
     return currentItem.time - nextItem.time > BROWSING_GAP_TIME &&
         currentItem.dateRelativeDay == nextItem.dateRelativeDay;
   };
 
   return { HistoryItem: HistoryItem };
 });