Add initial handshake reassembly tests.

For now, only test reorderings when we always or never fragment messages.
There's a third untested case: when full messages and fragments are mixed. That
will be tested later after making it actually work.

Change-Id: Ic4efb3f5e87b1319baf2d4af31eafa40f6a50fa6
Reviewed-on: https://boringssl-review.googlesource.com/3216
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/ssl/test/runner/common.go b/ssl/test/runner/common.go
index 99b0c04..3e37f1d 100644
--- a/ssl/test/runner/common.go
+++ b/ssl/test/runner/common.go
@@ -610,6 +610,12 @@
 
 	// PacketAdaptor is the packetAdaptor to use to simulate timeouts.
 	PacketAdaptor *packetAdaptor
+
+	// ReorderHandshakeFragments, if true, causes handshake fragments in
+	// DTLS to overlap and be sent in the wrong order. It also causes
+	// pre-CCS flights to be sent twice. (Post-CCS flights consist of
+	// Finished and will trigger a spurious retransmit.)
+	ReorderHandshakeFragments bool
 }
 
 func (c *Config) serverInit() {