[MD History] Make history-list:historyData private.

chrome/test/data/webui/md_history/history_item_test.js

Index: chrome/test/data/webui/md_history/history_item_test.js
diff --git a/chrome/test/data/webui/md_history/history_item_test.js b/chrome/test/data/webui/md_history/history_item_test.js
index ec011c8614c25b30288bccdc06bfe86e485dbcf7..bf89ff67855b25ce93bfb032b17d9acf45349ba0 100644
--- a/chrome/test/data/webui/md_history/history_item_test.js
+++ b/chrome/test/data/webui/md_history/history_item_test.js
@@ -66,16 +66,16 @@ cr.define('md_history.history_item_test', function() {
           var items =
               Polymer.dom(element.root).querySelectorAll('history-item');
 
-          element.set('historyData.3.selected', true);
+          element.set('historyData_.3.selected', true);
           items[3].onCheckboxSelected_();
 
           element.removeDeletedHistory(1);
-          assertEquals(element.historyData.length, 5);
+          assertEquals(element.historyData_.length, 5);
 
           // Checks that a new time gap separator has been inserted.
           assertTrue(items[2].hasTimeGap);
 
-          element.set('historyData.3.selected', true);
+          element.set('historyData_.3.selected', true);
           items[3].onCheckboxSelected_();
           element.removeDeletedHistory(1);
 
@@ -86,7 +86,7 @@ cr.define('md_history.history_item_test', function() {
       });
 
       teardown(function() {
-        element.historyData = [];
+        element.historyData_ = [];
         element.searchedTerm = '';
       });
     });