MD Downloads: track downloads in C++, dispatch discrete JS updates

chrome/test/data/webui/md_downloads/layout_tests.js

Index: chrome/test/data/webui/md_downloads/layout_tests.js
diff --git a/chrome/test/data/webui/md_downloads/layout_tests.js b/chrome/test/data/webui/md_downloads/layout_tests.js
index 7c09cf6ffb0950f1a228c5b4cf105ef7a2934783..e319b582f1125d66a90e629d591ae99cc9a3e91c 100644
--- a/chrome/test/data/webui/md_downloads/layout_tests.js
+++ b/chrome/test/data/webui/md_downloads/layout_tests.js
@@ -12,13 +12,14 @@ cr.define('downloads.layout_tests', function() {
         PolymerTest.clearBody();
         manager = document.createElement('downloads-manager');
         document.body.appendChild(manager);
+        assertEquals(manager, downloads.Manager.get());
       });
 
       test('long URLs ellide', function() {
-        manager.updateAll_([{
+        downloads.Manager.insertItems(0, [{
           file_name: 'file name',
           state: downloads.States.COMPLETE,
-          url: 'a'.repeat(10000),
+          url: 'a'.repeat(1000),
         }]);
 
         Polymer.dom.flush();