OEMCrypto v16.2

Merge from Widevine repo of http://go/wvgerrit/93404

This is the unit tests, reference code, and documentation for
OEMCrypto v16.2. Backwards compatibility should work for a v15
OEMCrypto.

Some review comments will be addressed in future CLs.

Bug: 141247171
Test: Unit tests
Test: Media GTS tests on bonito
Change-Id: I9d427c07580e180c0a4cfdc4a68f538d351c0ddd

libwvdrmengine/oemcrypto/odk/src/odk_util.h

@@ -0,0 +1,24 @@
+/* Copyright 2019 Google LLC. All rights reserved. This file and proprietary */
+/* source code may only be used and distributed under the Widevine Master */
+/* License Agreement. */
+
+#ifndef WIDEVINE_ODK_SRC_ODK_UTIL_H_
+#define WIDEVINE_ODK_SRC_ODK_UTIL_H_
+
+#include <stddef.h>
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* crypto_memcmp returns zero iff the |len| bytes at |a| and |b| are equal. It
+ * takes an amount of time dependent on |len|, but independent of the contents
+ * of |a| and |b|. Unlike memcmp, it cannot be used to order elements as the
+ * return value when a != b is undefined, other than being non-zero.  */
+int crypto_memcmp(const void* a, const void* b, size_t len);
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+#endif /* WIDEVINE_ODK_SRC_ODK_UTIL_H_ */