Certificate Transparency: Start tracking logs' state

net/cert/signed_tree_head.h

Index: net/cert/signed_tree_head.h
diff --git a/net/cert/signed_tree_head.h b/net/cert/signed_tree_head.h
index 154c7a9d08dad187e5b83e9ed238f579ace36845..f91f2934c6eeb3033a8267365dc2e91fcb41a092 100644
--- a/net/cert/signed_tree_head.h
+++ b/net/cert/signed_tree_head.h
@@ -50,10 +50,18 @@ struct NET_EXPORT SignedTreeHead {
   std::string log_id;
 };
 
+// Two STHs are considered equal if they are from the same log and have matching
+// timestamps, since RFC6962 forbids a log from issuing two different STHs with
+// the same timestamp.
+NET_EXPORT bool operator==(const SignedTreeHead& sth1,
+                           const SignedTreeHead& sth2);
+NET_EXPORT bool operator!=(const SignedTreeHead& sth1,
+                           const SignedTreeHead& sth2);
+
 NET_EXPORT void PrintTo(const SignedTreeHead& sth, std::ostream* os);
 
 }  // namespace ct
 
 }  // namespace net
 
-#endif
+#endif  // NET_CERT_SIGNED_TREE_HEAD_H_