Remove the crypto factories

pkg/crypto/lib/src/sha256.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.
 
 part of crypto;
 
-// The SHA256 hasher is used to compute an SHA256 message digest.
-class _SHA256 extends _HashBase implements SHA256 {
+/**
+ * SHA256 hash function implementation.
+ */
+class SHA256 extends _HashBase {
   // Construct a SHA256 hasher object.
-  _SHA256() : _w = new List(64), super(16, 8, true) {
+  SHA256() : _w = new List(64), super(16, 8, true) {
     // Initial value of the hash parts. First 32 bits of the fractional parts
     // of the square roots of the first 8 prime numbers.
     _h[0] = 0x6a09e667;
     _h[1] = 0xbb67ae85;
     _h[2] = 0x3c6ef372;
     _h[3] = 0xa54ff53a;
     _h[4] = 0x510e527f;
     _h[5] = 0x9b05688c;
     _h[6] = 0x1f83d9ab;
     _h[7] = 0x5be0cd19;
@@ skipping 75 matching lines @@
     _h[2] = _add32(c, _h[2]);
     _h[3] = _add32(d, _h[3]);
     _h[4] = _add32(e, _h[4]);
     _h[5] = _add32(f, _h[5]);
     _h[6] = _add32(g, _h[6]);
     _h[7] = _add32(h, _h[7]);
   }
 
   List<int> _w;
 }