Add CryptoUtils class.

tests/lib/crypto/sha256_test.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 tag to allow Dartium to run the tests.
 #library('sha256_test');
 
 // TODO(ager): Replace with "dart:crypto" when ready.
 #import("../../../lib/crypto/crypto.dart");
 
 #source('sha256_long_test_vectors.dart');
 #source('sha256_short_test_vectors.dart');
 
 List<int> createTestArr(int len) {
   var arr = new List<int>(len);
   for (var i = 0; i < len; i++) {
     arr[i] = i;
   }
   return arr;
 }
 
-String digestToString(List<int> digest) {
-  var buf = new StringBuffer();
-  for (var part in digest) {
-    buf.add("${(part < 16) ? "0" : ""}${part.toRadixString(16).toLowerCase()}");
-  }
-  return buf.toString();
-}
-
 void test() {
   final expected_values = const [
       'e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855',
       '6e340b9cffb37a989ca544e6bb780a2c78901d3fb33738768511a30617afa01d',
       'b413f47d13ee2fe6c845b2ee141af81de858df4ec549a58b7970bb96645bc8d2',
       'ae4b3280e56e2faf83f414a6e3dabe9d5fbe18976544c05fed121accb85b53fc',
       '054edec1d0211f624fed0cbca9d4f9400b0e491c43742af2c5b0abebf0c990d8',
       '08bb5e5d6eaac1049ede0893d30ed022b1a4d9b5b48db414871f51c9cb35283d',
       '17e88db187afd62c16e5debf3e6527cd006bc012bc90b51a810cd80c2d511f43',
       '57355ac3303c148f11aef7cb179456b9232cde33a818dfda2c2fcb9325749a6b',
@@ skipping 241 matching lines @@
       '552a69d052ae2980aa92ef44b4a8752fc585d70127d9df1ac53137e266786e4d',
       '369d7da16156c5e2c0d519cdbab3996a7249e20d3e48c36a3a873e987190bd89',
       'ef67e0723230f6c535ff556e45ca2174e1e97deed306e9e87f1b65579076ec06',
       '2cb1e75cd7505a2783769276f30b122cb136fbbd03300510b71a7196ca670b37',
       '1211b6885890be48f89934ec5246f1ce3cfff46c626cfcd686d5fdce9b1fb830',
       'd6a8bdb01e763fb64f3a02512e7be905679a5add6bb408f8750d679d17cad92f',
       '3f8591112c6bbe5c963965954e293108b7208ed2af893e500d859368c654eabe' ];
 
   for (var i = 0; i < expected_values.length; i++) {
     var d = new SHA256().update(createTestArr(i)).digest();
-    Expect.equals(expected_values[i], digestToString(d), '$i');
+    Expect.equals(expected_values[i], CryptoUtils.digestToHex(d), '$i');
   }
 }
 
 void testInvalidUse() {
   var sha = new SHA256();
   sha.digest();
   Expect.throws(() => sha.update([0]), (e) => e is HashException);
 }
 
 void testRepeatedDigest() {
   var sha = new SHA256();
   var digest = sha.digest();
   Expect.listEquals(digest, sha.digest());
 }
 
 void testStandardVectors(inputs, mds) {
   for (var i = 0; i < inputs.length; i++) {
     var d = new SHA256().update(inputs[i]).digest();
-    Expect.equals(mds[i], digestToString(d), '$i');
+    Expect.equals(mds[i], CryptoUtils.digestToHex(d), '$i');
   }
 }
 
 void main() {
   test();
   testInvalidUse();
   testRepeatedDigest();
   testStandardVectors(sha256_long_inputs, sha256_long_mds);
   testStandardVectors(sha256_short_inputs, sha256_short_mds);
 }