Added simplest device mount implementation (includes NullDevice and RandomDevice)

libraries/nacl-mounts/dev/Device.h

Index: libraries/nacl-mounts/dev/Device.h
===================================================================
--- libraries/nacl-mounts/dev/Device.h	(revision 0)
+++ libraries/nacl-mounts/dev/Device.h	(revision 0)
@@ -0,0 +1,22 @@
+/*
+ * Copyright (c) 2012 The Native Client Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+#ifndef PACKAGES_LIBRARIES_NACL_MOUNTS_DEV_DEVICE_H_
+#define PACKAGES_LIBRARIES_NACL_MOUNTS_DEV_DEVICE_H_
+
+#include <sys/types.h>
+#include "../util/macros.h"
+
+// Device
+class Device {
+ public:
+  Device() {}
+  virtual ~Device() {}
+  virtual int Read(off_t offset, void *buf, size_t count) = 0;
+  virtual int Write(off_t offset, const void *buf, size_t count) = 0;
+};
+
+#endif
+