Removed fixed dependencies

packages/crypto/lib/src/utils.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.
+
+/// A bitmask that limits an integer to 32 bits.
+const mask32 = 0xFFFFFFFF;
+
+/// The number of bits in a byte.
+const bitsPerByte = 8;
+
+/// The number of bytes in a 32-bit word.
+const bytesPerWord = 4;
+
+/// Adds [x] and [y] with 32-bit overflow semantics.
+int add32(int x, int y) => (x + y) & mask32;
+
+/// Bitwise rotates [val] to the left by [shift], obeying 32-bit overflow
+/// semantics.
+int rotl32(int val, int shift) {
+  var modShift = shift & 31;
+  return ((val << modShift) & mask32) | ((val & mask32) >> (32 - modShift));
+}