message: Replace direct references to the 'window' object with 'self' to allow usage in a service worker.
diff: @@ -50,7 +50,7 @@ class Hmac {
  * @static
  */
  static async newInstance(hash, key, tagSize) {
  - let cryptoKey = await window.crypto.subtle.importKey(
  + let cryptoKey = await self.crypto.subtle.importKey(
  'raw', key,
  {'name': 'HMAC', 'hash': {'name': hash}, 'length': key.length * 8},
  false, ['sign', 'verify']);
  @@ -63,7 +63,7 @@ class Hmac {
  */
  async computeMac(data) {
  Validators.requireUint8Array(data);
  - const tag = await window.crypto.subtle.sign(
  + const tag = await self.crypto.subtle.sign(
  {'name': 'HMAC', 'hash': {'name': this.hash_}}, this.key_, data);
  return new Uint8Array(tag.slice(0, this.tagSize_));
  }
  