Handle case where UDP packet contains multiple DTLS records.

webrtc/p2p/base/dtlstransportchannel_unittest.cc

Index: webrtc/p2p/base/dtlstransportchannel_unittest.cc
diff --git a/webrtc/p2p/base/dtlstransportchannel_unittest.cc b/webrtc/p2p/base/dtlstransportchannel_unittest.cc
index 4286d76be33bc37a9b7f694f31b93f79b348e64b..d886e3c488077d69a78893eaa3fd35ccc59f88f2 100644
--- a/webrtc/p2p/base/dtlstransportchannel_unittest.cc
+++ b/webrtc/p2p/base/dtlstransportchannel_unittest.cc
@@ -670,6 +670,15 @@ TEST_F(DtlsTransportChannelTest, TestTransferDtlsTwoChannels) {
   TestTransfer(1, 1000, 100, false);
 }
 
+// Connect with DTLS, combine multiple DTLS records into one packet.

[Taylor Brandstetter, 2017/07/06 22:06:11]

May be nice to have some context here; "Our DTLS implementation doesn't do this,
but other implementations may; see
https://tools.ietf.org/html/rfc6347#section-4.1.1."

Also, do you know what other implementations are known for doing this? Are they
not using OpenSSL/BoringSSL? Or are they using some option we don't know about?

[joachim, 2017/07/07 16:12:59]

Done
According to https://crbug.com/537189 this seems to be an interop problem with
ORTCLib (I mention this in the comment now). On their website
(http://ortclib.org/) they write about using OpenSSL for security, but I don't
know any details about their actual DTLS implementation.

+TEST_F(DtlsTransportChannelTest, TestTransferDtlsCombineRecords) {
+  PrepareDtls(true, true, rtc::KT_DEFAULT);
+  ASSERT_TRUE(Connect());
+  cricket::FakeIceTransport* transport = client1_.GetFakeIceTransort(0);
+  transport->set_combine(true);

[Taylor Brandstetter, 2017/07/06 22:06:11]

Would be nice to have a comment saying something like: "Our DTLS implementation
always sends one record per packet, so to simulate an endpoint that sends
multiple records per packet, we configure the fake ICE transport to combine
every two consecutive packets into a single packet."

[joachim, 2017/07/07 16:12:59]

Done.

+  TestTransfer(0, 500, 100, false);
+}
+
 // Connect with A doing DTLS and B not, and transfer some data.
 TEST_F(DtlsTransportChannelTest, TestTransferDtlsRejected) {
   PrepareDtls(true, false, rtc::KT_DEFAULT);