Move VideoTrackSourceProxy creation into VideoTrack.

This CL contains a part of a previously reviewed, landed, reverted,
relanded and re-reverted CL:
https://webrtc-review.googlesource.com/c/src/+/250180

Bug: webrtc:13540
Change-Id: Id6df8da5ff61e3ec90d0b3f3d828e8f670d4931b
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/251860
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Auto-Submit: Tomas Gunnarsson <tommi@webrtc.org>
Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#36025}

pc/BUILD.gn

@@ -1272,6 +1272,7 @@ rtc_library("video_track") {
     "video_track.h",
   ]
   deps = [
+    ":rtc_pc_base",
     "../api:media_stream_interface",
     "../api:scoped_refptr",
     "../api:sequence_checker",

pc/audio_track.h

@@ -21,6 +21,10 @@
 
 namespace webrtc {
 
+// TODO(tommi): Instead of inheriting from `MediaStreamTrack<>`, implement the
+// properties directly in this class. `MediaStreamTrack` doesn't guard against
+// conflicting access, so we'd need to override those methods anyway in this
+// class in order to make sure things are correctly checked.
 class AudioTrack : public MediaStreamTrack<AudioTrackInterface>,
                    public ObserverInterface {
  protected:

pc/video_rtp_receiver.cc

@@ -41,11 +41,7 @@ VideoRtpReceiver::VideoRtpReceiver(
       track_(VideoTrackProxyWithInternal<VideoTrack>::Create(
           rtc::Thread::Current(),
           worker_thread,
-          VideoTrack::Create(receiver_id,
+          VideoTrack::Create(receiver_id, source_, worker_thread))),
-                             CreateVideoTrackSourceProxy(rtc::Thread::Current(),
-                                                         worker_thread,
-                                                         source_),
-                             worker_thread))),
       attachment_id_(GenerateUniqueId()) {
   RTC_DCHECK(worker_thread_);
   SetStreams(streams);

pc/video_track.cc

@@ -23,12 +23,14 @@
 
 namespace webrtc {
 
-VideoTrack::VideoTrack(const std::string& label,
+VideoTrack::VideoTrack(
-                       VideoTrackSourceInterface* video_source,
+    const std::string& label,
+    rtc::scoped_refptr<
+        VideoTrackSourceProxyWithInternal<VideoTrackSourceInterface>> source,
     rtc::Thread* worker_thread)
     : MediaStreamTrack<VideoTrackInterface>(label),
       worker_thread_(worker_thread),
-      video_source_(video_source),
+      video_source_(std::move(source)),
       content_hint_(ContentHint::kNone) {
   RTC_DCHECK_RUN_ON(&signaling_thread_);
   // Detach the thread checker for VideoSourceBaseGuarded since we'll make calls
@@ -130,7 +132,13 @@ rtc::scoped_refptr<VideoTrack> VideoTrack::Create(
     const std::string& id,
     VideoTrackSourceInterface* source,
     rtc::Thread* worker_thread) {
-  return rtc::make_ref_counted<VideoTrack>(id, source, worker_thread);
+  rtc::scoped_refptr<
+      VideoTrackSourceProxyWithInternal<VideoTrackSourceInterface>>
+      source_proxy = VideoTrackSourceProxy::Create(rtc::Thread::Current(),
+                                                   worker_thread, source);
+
+  return rtc::make_ref_counted<VideoTrack>(id, std::move(source_proxy),
+                                           worker_thread);
 }
 
 }  // namespace webrtc

pc/video_track.h

@@ -22,11 +22,16 @@
 #include "api/video/video_source_interface.h"
 #include "media/base/video_source_base.h"
 #include "rtc_base/system/no_unique_address.h"
+#include "pc/video_track_source_proxy.h"
 #include "rtc_base/thread.h"
 #include "rtc_base/thread_annotations.h"
 
 namespace webrtc {
 
+// TODO(tommi): Instead of inheriting from `MediaStreamTrack<>`, implement the
+// properties directly in this class. `MediaStreamTrack` doesn't guard against
+// conflicting access, so we'd need to override those methods anyway in this
+// class in order to make sure things are correctly checked.
 class VideoTrack : public MediaStreamTrack<VideoTrackInterface>,
                    public rtc::VideoSourceBaseGuarded,
                    public ObserverInterface {
@@ -50,8 +55,10 @@ class VideoTrack : public MediaStreamTrack<VideoTrackInterface>,
   std::string kind() const override;
 
  protected:
-  VideoTrack(const std::string& id,
+  VideoTrack(
-             VideoTrackSourceInterface* video_source,
+      const std::string& id,
+      rtc::scoped_refptr<
+          VideoTrackSourceProxyWithInternal<VideoTrackSourceInterface>> source,
       rtc::Thread* worker_thread);
   ~VideoTrack();
 
@@ -61,7 +68,9 @@ class VideoTrack : public MediaStreamTrack<VideoTrackInterface>,
 
   RTC_NO_UNIQUE_ADDRESS webrtc::SequenceChecker signaling_thread_;
   rtc::Thread* const worker_thread_;
-  const rtc::scoped_refptr<VideoTrackSourceInterface> video_source_;
+  const rtc::scoped_refptr<
+      VideoTrackSourceProxyWithInternal<VideoTrackSourceInterface>>
+      video_source_;
   ContentHint content_hint_ RTC_GUARDED_BY(&signaling_thread_);
   // Cached `enabled` state for the worker thread. This is kept in sync with
   // the state maintained on the signaling thread via set_enabled() but can