Removed fixed dependencies

packages/crypto/lib/src/hash.dart

+// Copyright (c) 2015, 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.
+
+import 'dart:convert';
+
+import 'digest.dart';
+import 'digest_sink.dart';
+
+/// An interface for cryptographic hash functions.
+///
+/// Every hash is a converter that takes a list of ints and returns a single
+/// digest. When used in chunked mode, it will only ever add one digest to the
+/// inner [Sink].
+abstract class Hash extends Converter<List<int>, Digest> {
+  /// The internal block size of the hash in bytes.
+  ///
+  /// This is exposed for use by the `Hmac` class, which needs to know the block
+  /// size for the [Hash] it uses.
+  int get blockSize;
+
+  const Hash();
+
+  @override
+  Digest convert(List<int> data) {
+    var innerSink = new DigestSink();
+    var outerSink = startChunkedConversion(innerSink);
+    outerSink.add(data);
+    outerSink.close();
+    return innerSink.value;
+  }
+
+  @override
+  ByteConversionSink startChunkedConversion(Sink<Digest> sink);
+}