Add new view that renders local video using AVCaptureLayerPreview.

webrtc/base/objc/RTCDispatcher.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>
+
+typedef NS_ENUM(NSInteger, RTCDispatcherType) {

[tkchin_webrtc, 2015/12/07 18:27:07]

nit: RTCDispatchQueueType

otherwise it sounds like there are multiple ways to dispatch, as opposed to one
way to dispatch on multiple things

[Chuck, 2015/12/07 19:34:31]

Done.

+  // Main dispatcher queue.
+  RTCDispatcherTypeMain,

[tkchin_webrtc, 2015/12/07 18:27:07]

is this the main queue?

[Chuck, 2015/12/07 19:34:31]

Yes, seemed prudent to allow main queue through the same mechanism.

+  // Used for starting/stopping AVCaptureSession, and assigning
+  // capture session to AVCaptureVideoPreviewLayer.
+  RTCDispatcherTypeCaptureSession,
+};
+
+/** Dispatcher that asynchronously dispatches blocks to a specific
+ *  shared dispatch queue.
+ */
+@interface RTCDispatcher : NSObject
+

[tkchin_webrtc, 2015/12/07 18:27:07]

do we care about making init unavailable?

[Chuck, 2015/12/07 19:34:31]

Currently everything is static, so it shouldn't matter if someone creates an
instance. I'll make it unavailable for clarity.

+/** Dispatch the block asynchronously on the queue for dispatchType.
+ *  @param dispatchType The queue type to dispatch on.
+ *  @param block The block to dispatch asynchronously.
+ */
++ (void)dispatchAsyncOnType:(RTCDispatcherType)dispatchType
+                      block:(dispatch_block_t)block;
+
+@end