[MD History] Add full time hover text to dates in history items.

chrome/browser/resources/md_history/history_item.js

Index: chrome/browser/resources/md_history/history_item.js
diff --git a/chrome/browser/resources/md_history/history_item.js b/chrome/browser/resources/md_history/history_item.js
index e064ec6710efbb08bdb2ce0cd7a0d3f1e39c6ef5..f7a1df3dd59f76b341ae5e8c82ae3216c9472a92 100644
--- a/chrome/browser/resources/md_history/history_item.js
+++ b/chrome/browser/resources/md_history/history_item.js
@@ -300,6 +300,13 @@ cr.define('md_history', function() {
         return this.item.dateRelativeDay;
       return HistoryItem.searchResultsTitle(numberOfItems, search);
     },
+
+    /** @private */
+    addTimeTitle_: function() {
+      var el = this.$['time-accessed'];
+      el.setAttribute('title', new Date(this.item.time).toString());
+      this.unlisten(el, 'mouseover', 'addTimeTitle_');
+    },
   });
 
   /**