[MD History] Refactor history.html into a history-app element.

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

Index: chrome/test/data/webui/md_history/md_history_browsertest.js
diff --git a/chrome/test/data/webui/md_history/md_history_browsertest.js b/chrome/test/data/webui/md_history/md_history_browsertest.js
index a493c380a57f873c57093a37715e963cef2d10e7..c42ff675e2e72a30b7888d793a0d5d80049722e0 100644
--- a/chrome/test/data/webui/md_history/md_history_browsertest.js
+++ b/chrome/test/data/webui/md_history/md_history_browsertest.js
@@ -41,12 +41,8 @@ MaterialHistoryBrowserTest.prototype = {
     PolymerTest.prototype.setUp.call(this);
 
     suiteSetup(function() {
-      // Wait for each of the top-level elements to be upgraded.
-      return Promise.all([
-        waitForUpgrade($('history-list')),
-        waitForUpgrade($('toolbar')),
-        waitForUpgrade($('history-synced-device-manager')),
-      ]);
+      // Wait for the top-level app element to be upgraded.
+      return waitForUpgrade($('history-app'));
     });
   },
 };