[ci skip] Add license headers to externs

Author: dfreedm

externs/closure-types.js

@@ -1,4 +1,12 @@
-
+/**
+ * @license
+ * Copyright (c) 2017 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
+ */
 /**
  * @fileoverview Closure types for Polymer mixins
  *

externs/polymer-externs.js

@@ -1,4 +1,12 @@
 /**
+ * @license
+ * Copyright (c) 2017 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
+ *
  * @fileoverview Externs for Polymer
  * @externs
  */

externs/webcomponents-externs.js

@@ -1,4 +1,12 @@
 /**
+ * @license
+ * Copyright (c) 2017 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
+ *
  * @fileoverview Externs for webcomponents polyfills
  * @externs
  */

gulpfile.js

@@ -68,6 +68,17 @@ let CLOSURE_LINT_ONLY = false;
 
 let firstImportFinder = dom5.predicates.AND(dom5.predicates.hasTagName('link'), dom5.predicates.hasAttrValue('rel', 'import'));
 
+const licenseHeader =
+`/**
+ * @license
+ * Copyright (c) 2017 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
+ */`;
+
 class AddClosureTypeImport extends Transform {
   constructor(entryFileName, typeFileName) {
     super({objectMode: true});
@@ -241,6 +252,6 @@ gulp.task('lint', function() {
 gulp.task('generate-closure-externs', ['clean'], () => {
   let genClosure = require('@polymer/gen-closure-declarations').generateDeclarations;
   return genClosure().then((declarations) => {
-    fs.writeFileSync('externs/closure-types.js', declarations);
+    fs.writeFileSync('externs/closure-types.js', `${licenseHeader}${declarations}`);
   });
 });