Remove library dart:crypto

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;
 
 import "package:expect/expect.dart";
-import 'dart:crypto';
+import "package:crypto/crypto.dart";
 
 part 'sha256_long_test_vectors.dart';
 part '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;
@@ skipping 288 matching lines @@
 }
 
 void main() {
   test();
   testInvalidUse();
   testRepeatedDigest();
   testStandardVectors(sha256_long_inputs, sha256_long_mds);
   testStandardVectors(sha256_short_inputs, sha256_short_mds);
 }