Obj-C SDK Cleanup

This CL separates the files under sdk/objc into logical directories, replacing
the previous file layout under Framework/.

A long term goal is to have some system set up to generate the files under
sdk/objc/api (the PeerConnection API wrappers) from the C++ code. In the shorter
term the goal is to abstract out shared concepts from these classes in order to
make them as uniform as possible.

The separation into base/, components/, and helpers/ are to differentiate between
the base layer's common protocols, various utilities and the actual platform
specific components.

The old directory layout that resembled a framework's internal layout is not
necessary, since it is generated by the framework target when building it.

Bug: webrtc:9627
Change-Id: Ib084fd83f050ae980649ca99e841f4fb0580bd8f
Reviewed-on: https://webrtc-review.googlesource.com/94142
Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Rasmus Brandt <brandtr@webrtc.org>
Reviewed-by: Henrik Andreassson <henrika@webrtc.org>
Commit-Queue: Anders Carlsson <andersc@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24493}

sdk/objc/helpers/RTCDispatcher.h

@@ -0,0 +1,44 @@
+/*
+ *  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 "RTCMacros.h"
+
+typedef NS_ENUM(NSInteger, RTCDispatcherQueueType) {
+  // Main dispatcher queue.
+  RTCDispatcherTypeMain,
+  // Used for starting/stopping AVCaptureSession, and assigning
+  // capture session to AVCaptureVideoPreviewLayer.
+  RTCDispatcherTypeCaptureSession,
+  // Used for operations on AVAudioSession.
+  RTCDispatcherTypeAudioSession,
+};
+
+/** Dispatcher that asynchronously dispatches blocks to a specific
+ *  shared dispatch queue.
+ */
+RTC_EXPORT
+@interface RTCDispatcher : NSObject
+
+- (instancetype)init NS_UNAVAILABLE;
+
+/** 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:(RTCDispatcherQueueType)dispatchType block:(dispatch_block_t)block;
+
+/** Returns YES if run on queue for the dispatchType otherwise NO.
+ *  Useful for asserting that a method is run on a correct queue.
+ */
++ (BOOL)isOnQueueForType:(RTCDispatcherQueueType)dispatchType;
+
+@end