Use VideoSourceInterface for owning test video sources

CallTest, VideoQualityTest and VideoAnalyzer used test::TestVideoCapturer
as an interface for video sources. Change to use VideoSourceInterface instead,
since that's all they need.

This is a preparation for making test::VcmCapturer usable as a
VideoTrackSource, and replace use of cricket::VideoCapturer in example code.

Bug: webrtc:6353
Change-Id: I445f5f6f9b7342230b89f53a5722df9c9e92834f
Reviewed-on: https://webrtc-review.googlesource.com/c/114881
Commit-Queue: Niels Moller <nisse@webrtc.org>
Reviewed-by: Sebastian Jansson <srte@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26047}
diff --git a/test/call_test.cc b/test/call_test.cc
index 7a01079..80b86f0 100644
--- a/test/call_test.cc
+++ b/test/call_test.cc
@@ -63,7 +63,7 @@
   task_queue_.SendTask([this]() {
     fake_send_audio_device_ = nullptr;
     fake_recv_audio_device_ = nullptr;
-    video_capturers_.clear();
+    video_sources_.clear();
   });
 }
 
@@ -454,12 +454,10 @@
                                                      int width,
                                                      int height) {
   video_sources_.clear();
-  video_capturers_.clear();
   frame_generator_capturer_ = test::FrameGeneratorCapturer::Create(
       width, height, absl::nullopt, absl::nullopt, framerate * speed, clock);
-  video_capturers_.emplace_back(
+  video_sources_.emplace_back(
       std::unique_ptr<FrameGeneratorCapturer>(frame_generator_capturer_));
-  video_sources_.push_back(video_capturers_.back().get());
   ConnectVideoSourcesToStreams();
 }
 
@@ -467,12 +465,10 @@
                                             int width,
                                             int height) {
   video_sources_.clear();
-  video_capturers_.clear();
   frame_generator_capturer_ = test::FrameGeneratorCapturer::Create(
       width, height, absl::nullopt, absl::nullopt, framerate, clock_);
-  video_capturers_.emplace_back(
+  video_sources_.emplace_back(
       std::unique_ptr<FrameGeneratorCapturer>(frame_generator_capturer_));
-  video_sources_.push_back(video_capturers_.back().get());
   ConnectVideoSourcesToStreams();
 }
 
@@ -560,7 +556,7 @@
 
 void CallTest::ConnectVideoSourcesToStreams() {
   for (size_t i = 0; i < video_sources_.size(); ++i)
-    video_send_streams_[i]->SetSource(video_sources_[i],
+    video_send_streams_[i]->SetSource(video_sources_[i].get(),
                                       degradation_preference_);
 }