MD History: Delete button in the toolbar allows deletion of multiple history-items.

chrome/browser/resources/md_history/history_card.html

 <link rel="import" href="chrome://resources/polymer/v1_0/polymer/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-flex-layout/iron-flex-layout.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-styles/shadow.html">
 <link rel="import" href="chrome://history/history_item.html">
 
 <dom-module id="history-card">
   <template>
     <style>
       :host {
         @apply(--layout-center);
@@ skipping 39 matching lines @@
         <template is="dom-repeat" items="[[historyItems]]"
             as="historyItem">
           <history-item time-accessed_="[[historyItem.dateTimeOfDay]]"
               website-title_="[[historyItem.title]]"
               website-domain_="[[historyItem.domain]]"
               website-url_="[[historyItem.url]]"
               starred="[[historyItem.starred]]"
               selected="{{historyItem.selected}}"
               timestamp_="[[historyItem.time]]">
           </history-item>
-          <template is="dom-if" if="[[needsTimeGap_(index, historyItem)]]">
+          <template is="dom-if"
+              if="[[needsTimeGap_(index, historyItems.length)]]">

[calamity, 2016/02/02 05:34:58]

Does this function correctly if the actual item is changed then (i.e does
needsTimeGap_ run when the historyItems array length doesn't change but the
actual item being rendered does)? (This happens when cards are swapped in during
the infinite scroll, which is why we needed historyItem here in the first place)

#IfYouLikeItThenYouShouldHaveWroteATestForIt

[hsampson, 2016/02/02 22:59:53]

I haven't found any errors just scrolling but I think you are right here.

[calamity, 2016/02/03 02:10:50]

Can you write a regression test that recreates the issue and then verify that
having historyItem here fixes it?

             <div id="time-gap-separator"></div>
           </template>
         </template>
       </div>
     </div>
   </template>
   <script src="chrome://history/history_card.js"></script>
 </dom-module>