Add more externs

Add legacyWarnings and legacyNotifyOrder to externs

Author: dfreedm

externs/polymer-externs.js

@@ -141,6 +141,12 @@ Polymer.legacyUndefined;
 /** @type {boolean} */
 Polymer.legacyNoBatch;
 
+/** @type {boolean} */
+Polymer.legacyWarnings;
+
+/** @type {boolean} */
+Polymer.legacyNotifyOrder;
+
 // nb. This is explicitly 'var', as Closure Compiler checks that this is the case.
 /**
  * @constructor