audit license headers

Author: dfreedm

metadata.html

@@ -1,3 +1,12 @@
+<!--
+    @license
+    Copyright (c) 2014 The Polymer Project Authors. All rights reserved.
+    This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
+    The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
+    The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
+    Code distributed by Google as part of the polymer project is also
+    subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
+-->
 <x-meta id="core-icon" label="Icon" group="Core" hideSubtree>
 
   <template>