Add setting to AppRTCMobile for iOS, that can change capture resolution.

webrtc/examples/objc/AppRTCMobile/ios/ARDMediaConstraintsModel+Private.h

 /*
  *  Copyright 2016 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.
  */
 
-#include "webrtc/base/logging.h"
+#import <Foundation/Foundation.h>
+#import "ARDMediaConstraintsModel.h"
 
-#import <Foundation/Foundation.h>
+@class ARDMediaConstraintsSettingsStore;
 
-
-namespace rtc {
-std::string DescriptionFromOSStatus(OSStatus err) {
-  NSError* error =
-      [NSError errorWithDomain:NSOSStatusErrorDomain code:err userInfo:nil];
-  return error.description.UTF8String;
-}
-}  // namespace rtc
+NS_ASSUME_NONNULL_BEGIN
+@interface ARDMediaConstraintsModel ()
+- (ARDMediaConstraintsSettingsStore *)settingsStore;
+- (nullable NSString *)currentVideoResolutionWidthFromStore;
+- (nullable NSString *)currentVideoResolutionHeightFromStore;
+@end
+NS_ASSUME_NONNULL_END