Return proxied object in OnTransceiver

This makes it possible to invoke methods on the transceiver object
from any thread.

Also makes a few of the mock observer objects thread-safe, to allow
testing when the main thread is not the signaling thread.

Bug: webrtc:13183
Change-Id: Ic97efef71a21c3075700a028103061032f8d2bcc
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/232120
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#35010}
diff --git a/pc/sdp_offer_answer_unittest.cc b/pc/sdp_offer_answer_unittest.cc
new file mode 100644
index 0000000..df343cc
--- /dev/null
+++ b/pc/sdp_offer_answer_unittest.cc
@@ -0,0 +1,140 @@
+/*
+ *  Copyright 2017 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.
+ */
+
+#include <stdint.h>
+
+#include <memory>
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "absl/types/optional.h"
+#include "api/audio/audio_mixer.h"
+#include "api/audio_codecs/audio_decoder_factory.h"
+#include "api/audio_codecs/audio_encoder_factory.h"
+#include "api/audio_codecs/builtin_audio_decoder_factory.h"
+#include "api/audio_codecs/builtin_audio_encoder_factory.h"
+#include "api/create_peerconnection_factory.h"
+#include "api/jsep.h"
+#include "api/media_stream_interface.h"
+#include "api/media_types.h"
+#include "api/peer_connection_interface.h"
+#include "api/rtc_error.h"
+#include "api/rtp_parameters.h"
+#include "api/rtp_receiver_interface.h"
+#include "api/rtp_sender_interface.h"
+#include "api/rtp_transceiver_interface.h"
+#include "api/scoped_refptr.h"
+#include "api/set_remote_description_observer_interface.h"
+#include "api/uma_metrics.h"
+#include "api/video_codecs/builtin_video_decoder_factory.h"
+#include "api/video_codecs/builtin_video_encoder_factory.h"
+#include "api/video_codecs/video_decoder_factory.h"
+#include "api/video_codecs/video_encoder_factory.h"
+#include "media/base/stream_params.h"
+#include "modules/audio_device/include/audio_device.h"
+#include "modules/audio_processing/include/audio_processing.h"
+#include "p2p/base/port_allocator.h"
+#include "pc/media_session.h"
+#include "pc/peer_connection_wrapper.h"
+#include "pc/sdp_utils.h"
+#include "pc/session_description.h"
+#include "pc/test/fake_audio_capture_module.h"
+#include "pc/test/mock_peer_connection_observers.h"
+#include "rtc_base/checks.h"
+#include "rtc_base/gunit.h"
+#include "rtc_base/ref_counted_object.h"
+#include "rtc_base/rtc_certificate_generator.h"
+#include "rtc_base/thread.h"
+#include "system_wrappers/include/metrics.h"
+#include "test/gmock.h"
+#include "test/gtest.h"
+
+// This file contains unit tests that relate to the behavior of the
+// SdpOfferAnswer module.
+// Tests are writen as integration tests with PeerConnection, since the
+// behaviors are still linked so closely that it is hard to test them in
+// isolation.
+
+namespace webrtc {
+
+using RTCConfiguration = PeerConnectionInterface::RTCConfiguration;
+
+namespace {
+
+std::unique_ptr<rtc::Thread> CreateAndStartThread() {
+  auto thread = rtc::Thread::Create();
+  thread->Start();
+  return thread;
+}
+
+}  // namespace
+
+class SdpOfferAnswerTest : public ::testing::Test {
+ public:
+  SdpOfferAnswerTest()
+      // Note: We use a PeerConnectionFactory with a distinct
+      // signaling thread, so that thread handling can be tested.
+      : signaling_thread_(CreateAndStartThread()),
+        pc_factory_(
+            CreatePeerConnectionFactory(nullptr,
+                                        nullptr,
+                                        signaling_thread_.get(),
+                                        FakeAudioCaptureModule::Create(),
+                                        CreateBuiltinAudioEncoderFactory(),
+                                        CreateBuiltinAudioDecoderFactory(),
+                                        CreateBuiltinVideoEncoderFactory(),
+                                        CreateBuiltinVideoDecoderFactory(),
+                                        nullptr /* audio_mixer */,
+                                        nullptr /* audio_processing */)) {
+    webrtc::metrics::Reset();
+  }
+
+  std::unique_ptr<PeerConnectionWrapper> CreatePeerConnection() {
+    RTCConfiguration config;
+    config.sdp_semantics = SdpSemantics::kUnifiedPlan;
+    return CreatePeerConnection(config);
+  }
+
+  std::unique_ptr<PeerConnectionWrapper> CreatePeerConnection(
+      const RTCConfiguration& config) {
+    auto observer = std::make_unique<MockPeerConnectionObserver>();
+    auto pc = pc_factory_->CreatePeerConnection(config, nullptr, nullptr,
+                                                observer.get());
+    EXPECT_TRUE(pc.get());
+    observer->SetPeerConnectionInterface(pc.get());
+    return std::make_unique<PeerConnectionWrapper>(pc_factory_, pc,
+                                                   std::move(observer));
+  }
+
+ protected:
+  std::unique_ptr<rtc::Thread> signaling_thread_;
+  rtc::scoped_refptr<PeerConnectionFactoryInterface> pc_factory_;
+
+ private:
+};
+
+TEST_F(SdpOfferAnswerTest, OnTrackReturnsProxiedObject) {
+  auto caller = CreatePeerConnection();
+  auto callee = CreatePeerConnection();
+
+  auto audio_transceiver = caller->AddTransceiver(cricket::MEDIA_TYPE_AUDIO);
+
+  ASSERT_TRUE(caller->ExchangeOfferAnswerWith(callee.get()));
+  // Verify that caller->observer->OnTrack() has been called with a
+  // proxied transceiver object.
+  ASSERT_EQ(callee->observer()->on_track_transceivers_.size(), 1u);
+  auto transceiver = callee->observer()->on_track_transceivers_[0];
+  // Since the signaling thread is not the current thread,
+  // this will DCHECK if the transceiver is not proxied.
+  transceiver->stopped();
+}
+
+}  // namespace webrtc