Fix media_cas_proxy_sdk build issue.

Add example binary for testing building the SDK after 'git clone' from our repo.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=227583629

common/sha_util.cc

@@ -29,6 +29,14 @@ std::string Sha256_Hash(const std::string& message) {
   return digest;
 }
 
+std::string Sha512_Hash(const std::string& message) {
+  std::string digest;
+  digest.resize(SHA512_DIGEST_LENGTH);
+  SHA512(reinterpret_cast<const uint8_t*>(message.data()), message.size(),
+         reinterpret_cast<uint8_t*>(&digest[0]));
+  return digest;
+}
+
 std::string GenerateSha1Uuid(const std::string& name_space, const std::string& name) {
   // X.667 14 Setting the fields of a name-based UUID.
   // - Allocate a UUID to use as a "name space identifier" for all UUIDs