Initial patch from Will.

src/platform/cryptohome/entropy_source.h

+// Copyright (c) 2009-2010 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// EntropySource is the interface for objects that provide random bytes.
+
+#ifndef CRYPTOHOME_ENTROPY_SOURCE_H_
+#define CRYPTOHOME_ENTROPY_SOURCE_H_
+
+namespace cryptohome {
+
+class EntropySource {
+ public:
+  EntropySource() {}
+  virtual ~EntropySource() {}
+
+  virtual void GetSecureRandom(unsigned char *rand, int length) const = 0;
+};
+
+}  // namespace cryptohome
+
+#endif  // CRYPTOHOME_ENTROPY_SOURCE_H_