Init max supported H.264 profile at runtime on iOS

Bug: webrtc:9134, webrtc:7992
Change-Id: Id24c570bf3296298901f61ee817a3d7c3f8c6347
Reviewed-on: https://webrtc-review.googlesource.com/71560
Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
Commit-Queue: Kári Helgason <kthelgason@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23034}

sdk/objc/Framework/Classes/Video/UIDevice+H264Profile.h

@@ -0,0 +1,19 @@
+/*
+ *  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 <UIKit/UIKit.h>
+
+#include "media/base/h264_profile_level_id.h"
+
+@interface UIDevice (H264Profile)
+
++ (rtc::Optional<webrtc::H264::ProfileLevelId>)maxSupportedH264Profile;
+
+@end