fix(src): Add license headers

src/index.mjs

@@ -1,3 +1,19 @@
+/**
+ * Copyright 2018 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+**/
+
 import prefetchLinks from './prefetch.mjs';
 import requestIdleCallback from './request-idle-callback.mjs';
 

src/prefetch.mjs

@@ -53,6 +53,6 @@ const prefetchLinks = function (urls) {
   urls.forEach(url => {
     prefetch(url);
   });
-}
+};
 
 export default prefetchLinks;

src/request-idle-callback.mjs

@@ -1,3 +1,19 @@
+/**
+ * Copyright 2018 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+**/
+
 // RIC and shim for browsers setTimeout() without it
 const requestIdleCallback = window.requestIdleCallback ||
   function (cb) {