message: Add deriveBits function.
diff: }
  },
  + 'deriveBits': function(algorithm, baseKey, length) {
  + switch (mslCrypto$version) {
  + case WebCryptoVersion.LEGACY:
  + case WebCryptoVersion.V2014_01:
  + case WebCryptoVersion.V2014_02:
  + case WebCryptoVersion.V2014_02_SAFARI:
  + var op = nfCryptoSubtle.deriveBits(algorithm, baseKey, length);
  + return promisedOperation(op);
  + default:
  + throw new Error("Unsupported Web Crypto version " + mslCrypto$version + ".");
  + }
  + },
  +
  'importKey': function(format, keyData, algorithm, extractable, keyUsage) {
  var ext = normalizeExtractable(extractable);
  var ku = normalizeKeyUsage(keyUsage);
  