Adds function for generating MerkleTreeLeaf hash.

net/cert/merkle_tree_leaf.h

Index: net/cert/merkle_tree_leaf.h
diff --git a/net/cert/merkle_tree_leaf.h b/net/cert/merkle_tree_leaf.h
index efbe185713c6879afbe89c79ebfeb377e48f70fc..8f314f56a70641142300f8c6d556ab349178966b 100644
--- a/net/cert/merkle_tree_leaf.h
+++ b/net/cert/merkle_tree_leaf.h
@@ -42,6 +42,10 @@ NET_EXPORT bool GetMerkleTreeLeaf(const X509Certificate* cert,
                                   const SignedCertificateTimestamp* sct,
                                   MerkleTreeLeaf* merkle_tree_leaf);
 
+// Sets |*out| to the hash of the Merkle |tree_leaf|, as defined in RFC6962.
+// Returns true if the hash was generated, false if an error occurred.
+NET_EXPORT bool Hash(const MerkleTreeLeaf& tree_leaf, std::string* out);
+
 }  // namespace ct
 
 }  // namespace net