Support associated payload type when registering Rtx payload type.

Major changes include,
- Add associated payload type for SetRtxSendPayloadType & SetRtxReceivePayloadType.
- Receiver: Restore RTP packets by the new RTX-APT map.
- Sender: Send RTP packets by checking RTX-APT map.
- Add RTX payload type for RED in the default codec list.

BUG=4024
R=pbos@webrtc.org, stefan@webrtc.org
TBR=mflodman@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/26259004

Patch from Changbin Shao <changbin.shao@intel.com>.

git-svn-id: http://webrtc.googlecode.com/svn/trunk@8028 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/modules/rtp_rtcp/source/rtp_sender_unittest.cc

@@ -30,6 +30,7 @@ namespace {
 const int kTransmissionTimeOffsetExtensionId = 1;
 const int kAbsoluteSendTimeExtensionId = 14;
 const int kPayload = 100;
+const int kRtxPayload = 98;
 const uint32_t kTimestamp = 10;
 const uint16_t kSeqNum = 33;
 const int kTimeOffset = 22222;
@@ -654,6 +655,7 @@ TEST_F(RtpSenderTest, SendRedundantPayloads) {
   rtp_sender_.reset(new RTPSender(0, false, &fake_clock_, &transport, NULL,
                                   &mock_paced_sender_, NULL, NULL, NULL));
   rtp_sender_->SetSequenceNumber(kSeqNum);
+  rtp_sender_->SetRtxPayloadType(kRtxPayload, kPayload);
   // Make all packets go through the pacer.
   EXPECT_CALL(mock_paced_sender_,
               SendPacket(PacedSender::kNormalPriority, _, _, _, _, _)).
@@ -1123,7 +1125,7 @@ TEST_F(RtpSenderTest, BytesReportedCorrectly) {
   const uint8_t kPayloadType = 127;
   rtp_sender_->SetSSRC(1234);
   rtp_sender_->SetRtxSsrc(4321);
-  rtp_sender_->SetRtxPayloadType(kPayloadType - 1);
+  rtp_sender_->SetRtxPayloadType(kPayloadType - 1, kPayloadType);
   rtp_sender_->SetRTXStatus(kRtxRetransmitted | kRtxRedundantPayloads);
 
   ASSERT_EQ(