Remove use of PCH files in webrtc/sdk/objc

webrtc/sdk/objc/Framework/Headers/WebRTC/RTCNSGLVideoView.h

 /*
  *  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.
  */
 
+#import <Foundation/Foundation.h>
+
 #if !TARGET_OS_IPHONE
 
 #import <AppKit/NSOpenGLView.h>
 
 #import <WebRTC/RTCVideoRenderer.h>
 
 NS_ASSUME_NONNULL_BEGIN
 
 @class RTCNSGLVideoView;
 @protocol RTCNSGLVideoViewDelegate
 
 - (void)videoView:(RTCNSGLVideoView *)videoView didChangeVideoSize:(CGSize)size;
 
 @end
 
 @interface RTCNSGLVideoView : NSOpenGLView <RTCVideoRenderer>
 
 @property(nonatomic, weak) id<RTCNSGLVideoViewDelegate> delegate;
 
 @end
 
 NS_ASSUME_NONNULL_END
 
 #endif