Add support for Widevine ECM v3

Widevine ECM v3 is redesigned mainly based on protobuf, and supports new features including carrying fingerprinting and service blocking information. Existing clients must upgrade the Widevine CAS plugin to use the new ECM v3.

common/hash_algorithm.h

@@ -0,0 +1,18 @@
+////////////////////////////////////////////////////////////////////////////////
+// Copyright 2020 Google LLC.
+//
+// This software is licensed under the terms defined in the Widevine Master
+// License Agreement. For a copy of this agreement, please contact
+// widevine-licensing@google.com.
+////////////////////////////////////////////////////////////////////////////////
+
+#ifndef COMMON_HASH_ALGORITHM_H_
+#define COMMON_HASH_ALGORITHM_H_
+
+namespace widevine {
+
+enum class HashAlgorithm { kUnspecified, kSha1, kSha256 };
+
+}  // namespace widevine
+
+#endif  // COMMON_HASH_ALGORITHM_H_