Add base 64 encoding to the crypto library utils.

lib/crypto/crypto_vm.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // TODO(ager, iposva): Get rid of this file when the VM snapshot
 // generation can deal with normal library structure.
 
 #library('crypto');
 
 /**
@@ skipping 84 matching lines @@
  * Utility methods for working with message digests.
  */
 class CryptoUtils {
   /**
    * Convert a list of bytes (for example a message digest) into a hex
    * string.
    */
   static String bytesToHex(List<int> bytes) {
     return _CryptoUtils.bytesToHex(bytes);
   }
+
+  /**
+   * Converts a list of bytes (for example a message digest) into a
+   * base64 encoded string.
+   */
+  static String bytesToBase64(List<int> bytes) {
+    return _CryptoUtils.bytesToBase64(bytes);
+  }
 }
 
 /**
  * HashExceptions are thrown on invalid use of a Hash
  * object.
  */
 class HashException {
   HashException(String this.message);
   toString() => "HashException: $message";
   String message;
 }