message: Eliminate "inconsistent return type" errors related to async functions.
diff: @@ -43,7 +43,7 @@ const generateKeyPair = async function(curve) {
  const ephemeralKeyPair = await window.crypto.subtle.generateKey(
  ecdhParams, true /* extractable */,
  ['deriveKey', 'deriveBits'] /* usage */);
  - return ephemeralKeyPair;
  + return /** @type {!webCrypto.CryptoKey} */ (ephemeralKeyPair);
  };
  /**
  @@ -52,7 +52,7 @@ const generateKeyPair = async function(curve) {
  */
  const exportCryptoKey = async function(cryptoKey) {
  const jwk = await window.crypto.subtle.exportKey('jwk', cryptoKey);
  - return jwk;
  + return /** @type {!webCrypto.JsonWebKey} */ (jwk);
  };
  /**
  