message: Change MockRtpSender to not inherit from RefCountedObject.
  Cr-Commit-Position: refs/heads/main@{#36352}
diff: namespace webrtc {
  -class MockRtpSender : public rtc::RefCountedObject<RtpSenderInterface> {
  +class MockRtpSender : public RtpSenderInterface {
  public:
  + static rtc::scoped_refptr<MockRtpSender> Create() {
  + return rtc::make_ref_counted<MockRtpSender>();
  + }
  +
  MOCK_METHOD(bool, SetTrack, (MediaStreamTrackInterface*), (override));
  MOCK_METHOD(rtc::scoped_refptr<MediaStreamTrackInterface>,
  track,
  @@ -42,6 +46,7 @@ class MockRtpSender : public rtc::RefCountedObject<RtpSenderInterface> {
  (const, override));
  };
  +static_assert(!std::is_abstract_v<rtc::RefCountedObject<MockRtpSender>>, "");
  } // namespace webrtc
  #endif // API_TEST_MOCK_RTPSENDER_H_
  