message: Only use WebCrypto iff window.crypto and window.crypto.subtle are available.
diff: goog.module('tink.subtle.Environment');
  /** @const {boolean} */
  -const IS_WEBCRYPTO_AVAILABLE = (typeof goog.global['crypto']) !== 'undefined';
  +const IS_WEBCRYPTO_AVAILABLE = typeof goog.global['crypto'] !== 'undefined' &&
  + typeof goog.global['crypto']['subtle'] !== 'undefined';
  exports = {
  IS_WEBCRYPTO_AVAILABLE,
  