Datagram Transport Integration

- Implement datagram transport adaptor, which wraps datagram transport in DtlsTransportInternal. Datagram adaptor owns both ICE and Datagram Transports.
- Implement setup of datagram transport based on RTCConfiguration flag use_datagram_transport. This is very similar to MediaTransport setup with the exception that we create DTLS datagram adaptor.
- Propagate maximum datagram size to video encoder via MediaTransportConfig.

TODO: Currently this CL can only be tested in downstream projects. Once we add fake datagram transport, we will be able to implement unit tests similar to loopback media transport.

Bug: webrtc:9719
Change-Id: I4fa4a5725598dfee5da4f0f374269a7e289d48ed
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/138100
Commit-Queue: Anton Sukhanov <sukhanov@webrtc.org>
Reviewed-by: Bjorn Mellem <mellem@webrtc.org>
Reviewed-by: Steve Anton <steveanton@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#28047}

p2p/base/dtls_transport_internal.h

@@ -13,10 +13,13 @@
 
 #include <stddef.h>
 #include <stdint.h>
+
 #include <memory>
 #include <string>
 
 #include "api/crypto/crypto_options.h"
+#include "api/datagram_transport_interface.h"
+#include "api/dtls_transport_interface.h"
 #include "api/scoped_refptr.h"
 #include "p2p/base/ice_transport_internal.h"
 #include "p2p/base/packet_transport_internal.h"
@@ -41,6 +44,9 @@ enum DtlsTransportState {
   DTLS_TRANSPORT_FAILED,
 };
 
+webrtc::DtlsTransportState ConvertDtlsTransportState(
+    cricket::DtlsTransportState cricket_state);
+
 enum PacketFlags {
   PF_NORMAL = 0x00,       // A normal packet.
   PF_SRTP_BYPASS = 0x01,  // An encrypted SRTP packet; bypass any additional
@@ -59,6 +65,14 @@ class DtlsTransportInternal : public rtc::PacketTransportInternal {
 
   virtual const webrtc::CryptoOptions& crypto_options() const = 0;
 
+  // Returns datagram transport or nullptr if not using datagram transport.
+  // TODO(sukhanov): Make pure virtual.
+  // TODO(sukhanov): Consider moving ownership of datagram transport and ICE
+  // to JsepTransport.
+  virtual webrtc::DatagramTransportInterface* datagram_transport() {
+    return nullptr;
+  }
+
   virtual DtlsTransportState dtls_state() const = 0;
 
   virtual int component() const = 0;