Add iOS static library GN build script.

webrtc/sdk/objc/Framework/Classes/RTCVideoTrack.mm

 /*
  *  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 51 matching lines @@
     if (source) {
       _source = [[RTCVideoSource alloc] initWithNativeVideoSource:source.get()];
     }
   }
   return _source;
 }
 
 - (void)addRenderer:(id<RTCVideoRenderer>)renderer {
   // Make sure we don't have this renderer yet.
   for (RTCVideoRendererAdapter *adapter in _adapters) {
-    // Getting around unused variable error
-    if (adapter.videoRenderer != renderer) {
+    if (adapter.videoRenderer == renderer) {
       NSAssert(NO, @"|renderer| is already attached to this track");
+      return;
     }
   }
   // Create a wrapper that provides a native pointer for us.
   RTCVideoRendererAdapter* adapter =
       [[RTCVideoRendererAdapter alloc] initWithNativeRenderer:renderer];
   [_adapters addObject:adapter];
   self.nativeVideoTrack->AddOrUpdateSink(adapter.nativeVideoRenderer,
                                          rtc::VideoSinkWants());
 }
 
@@ skipping 16 matching lines @@
   [_adapters removeObjectAtIndex:indexToRemove];
 }
 
 #pragma mark - Private
 
 - (rtc::scoped_refptr<webrtc::VideoTrackInterface>)nativeVideoTrack {
   return static_cast<webrtc::VideoTrackInterface *>(self.nativeTrack.get());
 }
 
 @end