Implement md5 hash in crypto library.

lib/crypto/crypto.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.
 
 #library('crypto');
 
 #source('crypto_utils.dart');
+#source('hash_utils.dart');
 #source('hmac.dart');
-#source('sha_utils.dart');
+#source('md5.dart');
 #source('sha1.dart');
 #source('sha256.dart');
 
 /**
  * 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
@@ skipping 34 matching lines @@
 }
 
 /**
  * SHA256 hash function implementation.
  */
 interface SHA256 extends Hash default _SHA256 {
   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();
+}
+
+/**
  * 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 {
   /**
    * Create an [HMAC] object from a [Hash] and a key.
    */
   HMAC(Hash hash, List<int> key);
@@ skipping 26 matching lines @@
 /**
  * HashExceptions are thrown on invalid use of a Hash
  * object.
  */
 class HashException {
   HashException(String this.message);
   toString() => "HashException: $message";
   String message;
 }