Broadcast extension for AppRTCMobile on iOS

This provides an environment for testing out using WebRTC from an iOS
extension. It implements a ReplayKit broadcast extension for live
streaming games and screensharing.

The extension is only supported on iOS 11+ and is guarded by a build
flag.

Bug: webrtc:9335
Change-Id: Id218d6c73ef7599f5953c5a1e0e62e5d0dc4f10b
Reviewed-on: https://webrtc-review.googlesource.com/80000
Commit-Queue: Anders Carlsson <andersc@webrtc.org>
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23504}
diff --git a/examples/objc/AppRTCMobile/ios/broadcast_extension/ARDBroadcastSetupViewController.h b/examples/objc/AppRTCMobile/ios/broadcast_extension/ARDBroadcastSetupViewController.h
new file mode 100644
index 0000000..e95c5cc
--- /dev/null
+++ b/examples/objc/AppRTCMobile/ios/broadcast_extension/ARDBroadcastSetupViewController.h
@@ -0,0 +1,18 @@
+/*
+ *  Copyright 2018 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 <ReplayKit/ReplayKit.h>
+#import <UIKit/UIKit.h>
+
+API_AVAILABLE(ios(11.0))
+@interface ARDBroadcastSetupViewController
+    : UIViewController<UITextFieldDelegate>
+
+@end