Enabling 'gn check' on webrtc/sdk

webrtc/sdk/objc/Framework/Classes/RTCMetricsSampleInfo+Private.h

 /*
  *  Copyright 2016 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.
  */
 
 #import "WebRTC/RTCMetricsSampleInfo.h"
 
-#include "webrtc/system_wrappers/include/metrics_default.h"
+// Adding 'nogncheck' to disable the gn include headers check.
+// We don't want to depend on 'system_wrappers:metrics_default' because
+// clients should be able to provide their own implementation.
+#include "webrtc/system_wrappers/include/metrics_default.h"  // nogncheck
 
 NS_ASSUME_NONNULL_BEGIN
 
 @interface RTCMetricsSampleInfo ()
 
 /** Initialize an RTCMetricsSampleInfo object from native SampleInfo. */
 - (instancetype)initWithNativeSampleInfo:
     (const webrtc::metrics::SampleInfo &)info;
 
 @end
 
 NS_ASSUME_NONNULL_END