MD History: Add basic material design history cards and history items

chrome/browser/resources/md_history/history-card.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-card',

[Dan Beam, 2016/01/16 02:54:36]

nit: \n

[yingran, 2016/01/18 05:40:29]

Done.

+  properties: {
+    // The date of these history items.
+    historyDate: {
+      type: String,
+      value: ''
+    },
+    // The list of history results that were accessed for a particular day in
+    // reverse chronological order.
+    historyItems: {
+      type: Array,
+      value: []

[Dan Beam, 2016/01/16 02:54:36]

this should be:

  value: function() { return []; },

otherwise it'll be shared between instances (I think?)

[yingran, 2016/01/18 05:40:29]

Done.

+    }
+  },
+
+  /**
+   * Check whether the time difference between the given historyItem and the
+   * next one is large enough for a spacer to be required.
+   * @param {number} index The index number of the first item being compared.
+   * @return {boolean} Whether or not time gap separator is required.
+   * @private
+   */
+  needsTimeGap_: function(index) {
+    var items = this.historyItems;
+    return ((index + 1 < items.length) &&
+        (items[index].time - items[index + 1].time > BROWSING_GAP_TIME));

[Dan Beam, 2016/01/16 02:54:36]

isn't this equivalent to

return index + 1 < items.length &&
    items[index].time - items[index + 1].time > BROWSING_GAP_TIME;

[yingran, 2016/01/18 05:40:29]

yep

+  }
+});