Change the VM-specific crypto interfaces to asbstract classes.

runtime/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;
 
 import 'dart:math';
 
 /**
  * Interface for cryptographic hash functions.
  *
  * The [update] method is used to add data to the hash. The [digest] method
  * is used to extract the message digest.
  *
  * Once the [digest] method has been called no more data can be added using the
  * [update] method. If [update] is called after the first call to [digest] a
  * HashException is thrown.
  *
  * If multiple instances of a given Hash is needed the [newInstance]
  * method can provide a new instance.
  */
-interface Hash {
+abstract class Hash {
   /**
    * Add a list of bytes to the hash computation.
    */
   Hash update(List<int> data);
 
   /**
    * Finish the hash computation and extract the message digest as
    * a list of bytes.
    */
   List<int> digest();
 
   /**
    * Returns a new instance of this hash function.
    */
   Hash newInstance();
 
   /**
    * Block size of the hash in bytes.
    */
   int get blockSize;
 }
 
 /**
  * SHA1 hash function implementation.
  */
-interface SHA1 extends Hash default _SHA1 {
-  SHA1();
+abstract class SHA1 implements Hash {
+  factory SHA1() => new _SHA1();
 }
 
 /**
  * SHA256 hash function implementation.
  */
-interface SHA256 extends Hash default _SHA256 {
-  SHA256();
+abstract class SHA256 implements Hash {
+  factory SHA256() => new _SHA256();
 }
 
 /**
  * MD5 hash function implementation.
  *
  * WARNING: MD5 has known collisions and should only be used when
  * required for backwards compatibility.
  */
-interface MD5 extends Hash default _MD5 {
-  MD5();
+abstract class MD5 implements Hash {
+  factory MD5() => new _MD5();
 }
 
 /**
  * Hash-based Message Authentication Code support.
  *
  * The [update] method is used to add data to the message. The [digest] method
  * is used to extract the message authentication code.
  */
-interface HMAC default _HMAC {
+abstract class HMAC {
   /**
    * Create an [HMAC] object from a [Hash] and a key.
    */
-  HMAC(Hash hash, List<int> key);
+  factory HMAC(Hash hash, List<int> key) => new _HMAC(hash, key);
 
   /**
    * Add a list of bytes to the message.
    */
   HMAC update(List<int> data);
 
   /**
    * Perform the actual computation and extract the message digest
    * as a list of bytes.
    */
   List<int> digest();
 }
 
 /**
  * Utility methods for working with message digests.
  */
-class CryptoUtils {
+abstract 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 optionally broken up in to lines of
    * [lineLength] chars separated by '\r\n'.
    */
   static String bytesToBase64(List<int> bytes, [int lineLength]) {
     return _CryptoUtils.bytesToBase64(bytes, lineLength);
   }
 }
 
 /**
  * HashExceptions are thrown on invalid use of a Hash
  * object.
  */
 class HashException {
   HashException(String this.message);
   toString() => "HashException: $message";
   String message;
 }