Don't expire certs used as channel IDs.

net/ssl/server_bound_cert_service.h

Index: net/ssl/server_bound_cert_service.h
diff --git a/net/ssl/server_bound_cert_service.h b/net/ssl/server_bound_cert_service.h
index 734199e3471c0981fe9f5dda91cabaea5534276a..6663fade88b96abe9d6d23b664a0c81ec5259978 100644
--- a/net/ssl/server_bound_cert_service.h
+++ b/net/ssl/server_bound_cert_service.h
@@ -29,7 +29,14 @@ class ServerBoundCertServiceJob;
 class ServerBoundCertServiceRequest;
 class ServerBoundCertServiceWorker;
 
-// A class for creating and fetching server bound certs.
+// A class for creating and fetching server bound certs. These certs are used
+// to identify users' machines; their public keys are used as channel IDs in
+// http://tools.ietf.org/html/draft-balfanz-tls-channelid-00.
+// As a result although certs are set to be invalid after one year, we don't
+// actually expire them. Once generated, certs are valid as long as the users
+// want. Users can delete existing certs, and new certs will be generated
+// automatically.
+
 // Inherits from NonThreadSafe in order to use the function
 // |CalledOnValidThread|.
 class NET_EXPORT ServerBoundCertService