Adds a function for encoding a Merkle tree leaf in TLS wire format.

net/cert/ct_serialization.h

Index: net/cert/ct_serialization.h
diff --git a/net/cert/ct_serialization.h b/net/cert/ct_serialization.h
index fa7ab0c6d45c411403c60c6acb81df918043f971..269892d3512d7a675e84174061a5bed8969bb040 100644
--- a/net/cert/ct_serialization.h
+++ b/net/cert/ct_serialization.h
@@ -21,6 +21,7 @@ namespace ct {
 
 struct DigitallySigned;
 struct LogEntry;
+struct MerkleTreeLeaf;
 struct SignedCertificateTimestamp;
 struct SignedTreeHead;
 
@@ -40,6 +41,12 @@ NET_EXPORT_PRIVATE bool DecodeDigitallySigned(base::StringPiece* input,
 NET_EXPORT_PRIVATE bool EncodeLogEntry(const LogEntry& input,
                                        std::string* output);
 
+// Serialises the Merkle tree |leaf|, appending it to |output|.
+// These bytes can be hashed for use with audit proof fetching.
+// Note that |leaf.log_id| is not part of the TLS encoding, and so will not be
+// serialized.
+NET_EXPORT bool EncodeTreeLeaf(const MerkleTreeLeaf& leaf, std::string* output);
+
 // Encodes the data signed by a Signed Certificate Timestamp (SCT) into
 // |output|. The signature included in the SCT is then verified over these
 // bytes.