Implemented the GetSources() in native code.

webrtc/pc/peerconnection_unittest.cc

 /*
  *  Copyright 2012 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 2620 matching lines @@
                webrtc::PeerConnectionInterface::kIceConnectionConnected ||
            initializing_client()->ice_connection_state() ==
                webrtc::PeerConnectionInterface::kIceConnectionCompleted),
       total_connection_time_ms, fake_clock);
   // Need to free the clients here since they're using things we created on
   // the stack.
   delete set_initializing_client(nullptr);
   delete set_receiving_client(nullptr);
 }
 
+// The end to end test of the method GetContributingSources(). Tests the
+// function calling chain from API layer down to the rtp_rtcp module.
+TEST_F(P2PTestConductor, TestGetContributingSources) {

[Taylor Brandstetter, 2017/03/30 22:55:38]

I recently refactored the tests in this file, FYI. There's no more
"LocalP2PTest", so you'll have to explicitly add an audio track to the caller's
PeerConnection.

[Zhi Huang, 2017/03/31 06:44:05]

Acknowledged.

+  ASSERT_TRUE(CreateTestClients());
+  LocalP2PTest();
+
+  ASSERT_GT(receiving_client()->pc()->GetReceivers().size(), 0);
+  auto receiver = receiving_client()->pc()->GetReceivers()[0];
+  ASSERT_EQ(receiver->media_type(), cricket::MEDIA_TYPE_AUDIO);
+
+  auto contributing_sources = receiver->GetContributingSources();
+  ASSERT_GT(receiver->GetParameters().encodings.size(), 0);
+  EXPECT_EQ(receiver->GetParameters().encodings[0].ssrc,
+            contributing_sources[0]->source());
+}
+
 class IceServerParsingTest : public testing::Test {
  public:
   // Convenience for parsing a single URL.
   bool ParseUrl(const std::string& url) {
     return ParseUrl(url, std::string(), std::string());
   }
 
   bool ParseTurnUrl(const std::string& url) {
     return ParseUrl(url, "username", "password");
   }
@@ skipping 209 matching lines @@
   servers.push_back(server);
   EXPECT_EQ(webrtc::RTCErrorType::NONE,
             webrtc::ParseIceServers(servers, &stun_servers_, &turn_servers_));
   EXPECT_EQ(2U, turn_servers_.size());
   EXPECT_NE(turn_servers_[0].priority, turn_servers_[1].priority);
 }
 
 #endif // if !defined(THREAD_SANITIZER)
 
 }  // namespace