Add DTLS support to NSS, contributed by Eric Rescorla.

net/third_party/nss/ssl/sslsecur.c

Index: net/third_party/nss/ssl/sslsecur.c
===================================================================
--- net/third_party/nss/ssl/sslsecur.c	(revision 127709)
+++ net/third_party/nss/ssl/sslsecur.c	(working copy)
@@ -615,6 +615,7 @@
     if (!(flags & PR_MSG_PEEK)) {
 	ss->gs.readOffset += amount;
     }
+    PORT_Assert(ss->gs.readOffset <= ss->gs.writeOffset);

[wtc, 2012/03/21 23:12:16]

Nit: should we assert the invariant before the return
statement?  Or is it only safe to asser the invariant when
the function returns successfully?

I can see here is a good place to assert because we just
updated ss->gs.readOffset.

[ekr, 2012/03/22 15:07:17]

I'm not sure about the first question, but your last statement seems plausible.

     rv = amount;
 
     SSL_TRC(30, ("%d: SSL[%d]: amount=%d available=%d",