Update call expectations in ReceiveStatisticsProxy, add thread checks

Bug: chromium:1084619
Change-Id: If9042d44ad99eacd431ee2a5e84486cfaf282d7e
Tbr: stefan@webrtc.org
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/175658
Reviewed-by: Tommi <tommi@webrtc.org>
Commit-Queue: Tommi <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31330}

modules/video_coding/frame_buffer2.h

@@ -28,6 +28,7 @@
 #include "rtc_base/event.h"
 #include "rtc_base/experiments/rtt_mult_experiment.h"
 #include "rtc_base/numerics/sequence_number_util.h"
+#include "rtc_base/synchronization/sequence_checker.h"
 #include "rtc_base/task_queue.h"
 #include "rtc_base/task_utils/repeating_task.h"
 #include "rtc_base/thread_annotations.h"
@@ -159,6 +160,9 @@ class FrameBuffer {
   EncodedFrame* CombineAndDeleteFrames(
       const std::vector<EncodedFrame*>& frames) const;
 
+  SequenceChecker construction_checker_;
+  SequenceChecker callback_checker_;
+
   // Stores only undecoded frames.
   FrameMap frames_ RTC_GUARDED_BY(crit_);
   DecodedFramesHistory decoded_frames_history_ RTC_GUARDED_BY(crit_);