Don't assume we have a worker_thread_ on linux (for now)

Tbr: mbonadei@webrtc.org
No-Try: true
Bug: none
Change-Id: I0dca1e54b610b63651235a83ec80f0e7d76f51c4
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/173085
Reviewed-by: Tommi <tommi@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Tommi <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31019}

video/receive_statistics_proxy.cc

@@ -769,6 +769,7 @@ void ReceiveStatisticsProxy::OnTimingFrameInfoUpdated(
 void ReceiveStatisticsProxy::RtcpPacketTypesCounterUpdated(
     uint32_t ssrc,
     const RtcpPacketTypeCounter& packet_counter) {
+#if !defined(WEBRTC_LINUX)
   if (!worker_thread_->IsCurrent()) {
     // RtpRtcp::Configuration has a single RtcpPacketTypeCounterObserver and
     // that same configuration may be used for both receiver and sender
@@ -791,6 +792,7 @@ void ReceiveStatisticsProxy::RtcpPacketTypesCounterUpdated(
   }
 
   RTC_DCHECK_RUN_ON(&main_thread_);
+#endif
   rtc::CritScope lock(&crit_);
   if (stats_.ssrc != ssrc)
     return;