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 2a69bc4a3a77abac4121a6f0ff39056d09ff6825..2e146c57459cf53cfb2dcbeb37e1f5e950484356 100644
--- a/net/cert/merkle_tree_leaf.h
+++ b/net/cert/merkle_tree_leaf.h
@@ -30,6 +30,10 @@ struct NET_EXPORT MerkleTreeLeaf {
   MerkleTreeLeaf();
   ~MerkleTreeLeaf();
 
+  // Sets |*out| to the hash of this Merkle tree leaf, as defined in RFC6962.
+  // Returns true if the hash was generated, false if an error occurred.
+  bool Hash(std::string* out) const;
+
   // Version and Merkle leaf type fields are omitted, as there is only one
   // possible value for each of them in CTv1.