Address tkchin's comments on RTCCameraVideoCapturer.

webrtc/sdk/objc/Framework/Classes/RTCDispatcher.m

 /*
  *  Copyright 2015 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 15 matching lines @@
         DISPATCH_QUEUE_SERIAL);
   });
 }
 
 + (void)dispatchAsyncOnType:(RTCDispatcherQueueType)dispatchType
                       block:(dispatch_block_t)block {
   dispatch_queue_t queue = [self dispatchQueueForType:dispatchType];
   dispatch_async(queue, block);
 }
 
++ (BOOL)isOnQueueForType:(RTCDispatcherQueueType)dispatchType {
+  dispatch_queue_t targetQueue = [self dispatchQueueForType:dispatchType];
+  const char* targetLabel = dispatch_queue_get_label(targetQueue);
+  const char* currentLabel = dispatch_queue_get_label(DISPATCH_CURRENT_QUEUE_LABEL);
+
+  NSAssert(strlen(targetLabel) > 0, @"Label is required for the target queue.");
+  NSAssert(strlen(currentLabel) > 0, @"Label is required for the current queue.");
+
+  return strcmp(targetLabel, currentLabel) == 0;
+}
+
 #pragma mark - Private
 
 + (dispatch_queue_t)dispatchQueueForType:(RTCDispatcherQueueType)dispatchType {
   switch (dispatchType) {
     case RTCDispatcherTypeMain:
       return dispatch_get_main_queue();
     case RTCDispatcherTypeCaptureSession:
       return kCaptureSessionQueue;
     case RTCDispatcherTypeAudioSession:
       return kAudioSessionQueue;
   }
 }
 
 @end