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.c

@@ -0,0 +1,25 @@
+/* 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. */
+
+#include "odk_util.h"
+
+int crypto_memcmp(const void* in_a, const void* in_b, size_t len) {
+  if (len == 0) {
+    return 0;
+  }
+
+  /* Only valid pointers are allowed. */
+  if (in_a == NULL || in_b == NULL) {
+    return -1;
+  }
+
+  const uint8_t* a = in_a;
+  const uint8_t* b = in_b;
+  uint8_t x = 0;
+
+  for (size_t i = 0; i < len; i++) {
+    x |= a[i] ^ b[i];
+  }
+  return x;
+}