Add video codec setting to AppRTCMobile on iOS.

webrtc/examples/objc/AppRTCMobile/ios/ARDSettingsModel.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.
  */
 
@@ skipping 31 matching lines @@
  * Stores the provided video resolution media constraint string into the store.
  *
  * If the provided constraint is no part of the available video resolutions
  * the store operation will not be executed and NO will be returned.
  * @param constraint the string to be stored.
  * @return YES/NO depending on success.
  */
 - (BOOL)storeVideoResoultionConstraint:(NSString *)constraint;
 
 /**
+ * Returns array of available video codecs.
+ */
+- (NSArray<NSString *> *)availableVideoCodecs;
+
+/**
+ * Returns current video codec setting from store if present.

[daniela-webrtc, 2017/03/20 13:10:06]

This documentation can be improved slightly. Suggestion:
"Returns current video codec setting from store if present or default (H264)
otherwise".

+ */
+- (NSString *)currentVideoCodecSettingFromStore;
+
+/**
+ * Stores the provided video codec setting into the store.
+ *
+ * If the provided constraint is not part of the available video codecs

[daniela-webrtc, 2017/03/20 13:10:07]

provided constraint -> provided video codec

+ * the store operation will not be executed and NO will be returned.
+ * @param video codec settings the string to be stored.
+ * @return YES/NO depending on success.
+ */
+- (BOOL)storeVideoCodecSetting:(NSString *)videoCodec;
+
+/**
  * Converts the current media constraints from store into dictionary with RTCMediaConstraints
  * values.
  *
  * @return NSDictionary with RTC width and height parameters
  */
 - (nullable NSDictionary *)currentMediaConstraintFromStoreAsRTCDictionary;
 
 /**
  * Returns current max bitrate setting from store if present.
  */
 - (nullable NSNumber *)currentMaxBitrateSettingFromStore;
 
 /**
  * Stores the provided bitrate value into the store.
  *
  * @param bitrate NSNumber representation of the max bitrate value.
  */
 - (void)storeMaxBitrateSetting:(nullable NSNumber *)bitrate;
 
 @end
 NS_ASSUME_NONNULL_END