Updates to VCMDecodedFrameCallback, VideoReceiver and a few related classes/tests.

webrtc/modules/video_coding/video_coding_impl.cc

Index: webrtc/modules/video_coding/video_coding_impl.cc
diff --git a/webrtc/modules/video_coding/video_coding_impl.cc b/webrtc/modules/video_coding/video_coding_impl.cc
index c53a68796593cb491de89fb8e0328eee58a98d57..26c47781adf741b38130ca3eff2074db8b9bf5da 100644
--- a/webrtc/modules/video_coding/video_coding_impl.cc
+++ b/webrtc/modules/video_coding/video_coding_impl.cc
@@ -14,6 +14,7 @@
 #include <utility>
 
 #include "webrtc/base/criticalsection.h"
+#include "webrtc/base/thread_checker.h"
 #include "webrtc/common_types.h"
 #include "webrtc/common_video/include/video_bitrate_allocator.h"
 #include "webrtc/common_video/libyuv/include/webrtc_libyuv.h"
@@ -190,6 +191,7 @@ class VideoCodingModuleImpl : public VideoCodingModule {
 
   int32_t RegisterReceiveCallback(
       VCMReceiveCallback* receiveCallback) override {
+    RTC_DCHECK(construction_thread_.CalledOnValidThread());
     return receiver_.RegisterReceiveCallback(receiveCallback);
   }
 
@@ -210,6 +212,7 @@ class VideoCodingModuleImpl : public VideoCodingModule {
 
   int32_t RegisterPacketRequestCallback(
       VCMPacketRequestCallback* callback) override {
+    RTC_DCHECK(construction_thread_.CalledOnValidThread());
     return receiver_.RegisterPacketRequestCallback(callback);
   }
 
@@ -277,6 +280,7 @@ class VideoCodingModuleImpl : public VideoCodingModule {
   void TriggerDecoderShutdown() override { receiver_.TriggerDecoderShutdown(); }
 
  private:
+  rtc::ThreadChecker construction_thread_;
   EncodedImageCallbackWrapper post_encode_callback_;
   vcm::VideoSender sender_;
   std::unique_ptr<VideoBitrateAllocator> rate_allocator_;