Add new view that renders local video using AVCaptureLayerPreview.

talk/app/webrtc/objc/RTCCameraPreviewView.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.
+ */
+#if !defined(__has_feature) || !__has_feature(objc_arc)

[tkchin_webrtc, 2015/12/04 22:19:42]

nit: add blank line

[Chuck, 2015/12/05 00:21:23]

Done.

+#error "This file requires ARC support."
+#endif
+
+#import "RTCCameraPreviewView.h"
+
+#import <AVFoundation/AVFoundation.h>
+
+#import "RTCAVFoundationVideoSource+Internal.h"
+
+@implementation RTCCameraPreviewView
+
+@synthesize videoSource = _videoSource;
+
++ (Class)layerClass {
+  return [AVCaptureVideoPreviewLayer class];
+}
+
+

[tkchin_webrtc, 2015/12/04 22:19:41]

nit: remove blank line

[Chuck, 2015/12/05 00:21:23]

Done.

+- (void)setVideoSource:(RTCAVFoundationVideoSource *)videoSource {
+  if (_videoSource == videoSource) {

[tkchin_webrtc, 2015/12/04 22:19:41]

Suggest not making this class depend on that particular video source, since we
only really need it just for the dispatch queue. Think this points at making a
common dispatch queue file.

[Chuck, 2015/12/05 00:21:23]

Done.

+    return;
+  }
+  _videoSource = videoSource;
+  AVCaptureSession *captureSession = videoSource.captureSession;
+  AVCaptureVideoPreviewLayer *previewLayer = [self previewLayer];
+  if (!videoSource) {
+    previewLayer.session = nil;
+    return;
+  }
+  dispatch_async(videoSource.captureSessionQueue, ^{
+    previewLayer.session = captureSession;
+  });
+}
+
+#pragma mark - Private
+
+- (AVCaptureVideoPreviewLayer *)previewLayer {
+  return (AVCaptureVideoPreviewLayer *)self.layer;
+}
+
+@end