Refactor

This renames the "mock" code to "reference" because that's really what
it is.  Also, some code has been moved from the CDM repo to a common
utility directory so that it can be included here, and the oemcrypto
unit tests can now be built without having access to a current CDM
repo.

There are no functionality changes in this CL.

util/include/clock.h

@@ -0,0 +1,24 @@
+// Copyright 2013 Google Inc. All Rights Reserved.
+//
+// Clock - Platform independent interface for a time library
+//
+#ifndef WVCDM_UTIL_CLOCK_H_
+#define WVCDM_UTIL_CLOCK_H_
+
+#include <stdint.h>
+
+namespace wvcdm {
+
+// Provides time related information. The implementation is platform dependent.
+class Clock {
+ public:
+  Clock() {}
+  virtual ~Clock() {}
+
+  // Provides the number of seconds since an epoch - 01/01/1970 00:00 UTC
+  virtual int64_t GetCurrentTime();
+};
+
+}  // namespace wvcdm
+
+#endif  // WVCDM_UTIL_CLOCK_H_