Fix build

protos/public/hash_algorithm.proto

@@ -0,0 +1,20 @@
+////////////////////////////////////////////////////////////////////////////////
+// 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.
+////////////////////////////////////////////////////////////////////////////////
+
+syntax = "proto3";
+
+package widevine;
+
+// LINT.IfChange
+enum HashAlgorithmProto {
+  // Unspecified hash algorithm: SHA_256 shall be used for ECC based algorithms
+  // and SHA_1 shall be used otherwise.
+  HASH_ALGORITHM_UNSPECIFIED = 0;
+  HASH_ALGORITHM_SHA_1 = 1;
+  HASH_ALGORITHM_SHA_256 = 2;
+}