AppRTCMobile iOS: Use video encoder factory to manage codec preference.

List codecs from factory in settings, select by changing order in factory.

Bug: webrtc:7925
Change-Id: If3c45e56713104c88705c67560325d002e6d6700
Reviewed-on: https://webrtc-review.googlesource.com/3720
Commit-Queue: Anders Carlsson <andersc@webrtc.org>
Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20312}

examples/objc/AppRTCMobile/ios/RTCVideoCodecInfo+HumanReadable.h

@@ -0,0 +1,17 @@
+/*
+ *  Copyright 2017 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 "WebRTC/RTCVideoCodec.h"
+
+@interface RTCVideoCodecInfo (HumanReadable)
+
+- (NSString *)humanReadableDescription;
+
+@end