diff --git a/clock_interface.h b/clock_interface.h
new file mode 100644
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--- /dev/null
+++ b/clock_interface.h
@@ -0,0 +1,35 @@
+// Copyright (c) 2013 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.
+
+#ifndef CHROMEOS_PLATFORM_UPDATE_ENGINE_CLOCK_INTERFACE_H__
+#define CHROMEOS_PLATFORM_UPDATE_ENGINE_CLOCK_INTERFACE_H__
+
+#include <string>
+
+#include <base/time.h>
+
+namespace chromeos_update_engine {
+
+// The clock interface allows access to various system clocks. The
+// sole reason for providing this as an interface is unit testing.
+// Additionally, the sole reason for the methods not being static
+// is also unit testing.
+class ClockInterface {
+ public:
+  // Gets the current time e.g. similar to base::Time::Now().
+  virtual base::Time GetWallclockTime() = 0;
+
+  // Returns monotonic time since some unspecified starting point. It
+  // is not increased when the system is sleeping nor is it affected
+  // by NTP or the user changing the time.
+  //
+  // (This is a simple wrapper around clock_gettime(2) / CLOCK_MONOTONIC_RAW.)
+  virtual base::Time GetMonotonicTime() = 0;
+
+  virtual ~ClockInterface() {}
+};
+
+}  // namespace chromeos_update_engine
+
+#endif  // CHROMEOS_PLATFORM_UPDATE_ENGINE_CLOCK_INTERFACE_H__