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.h

@@ -21,6 +21,9 @@ std::string Sha1_Hash(const std::string& message);
 // Calculates SHA256 hash.
 std::string Sha256_Hash(const std::string& message);
 
+// Calculate SHA512 hash.
+std::string Sha512_Hash(const std::string& message);
+
 // Generates a UUID as specified in ITU-T X.667 ch. 14, SHA-1 name-based,
 // 16-byte binary representation. Name_space is a GUID prefix; name is a unique
 // name in the namespace.