Add new view that renders local video using AVCaptureLayerPreview.

webrtc/base/objc/RTCCameraPreviewView.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>
+#import <UIKit/UIKit.h>
+
+@class AVCaptureSession;
+@class RTCAVFoundationVideoSource;
+
+/** RTCCameraPreviewView is a view that renders local video from an
+ *  AVCaptureSession.
+ */
+@interface RTCCameraPreviewView : UIView
+
+/** The capture session being rendered in the view. Capture session
+ *  is assigned to AVCaptureVideoPreviewLayer async in the same
+ *  queue that the AVCaptureSession is started/stopped.
+ */
+@property(nonatomic, strong) AVCaptureSession *captureSession;
+
+@end