Add video codec setting to AppRTCMobile on iOS.

webrtc/examples/objc/AppRTCMobile/ios/ARDSettingsModel.h

Index: webrtc/examples/objc/AppRTCMobile/ios/ARDSettingsModel.h
diff --git a/webrtc/examples/objc/AppRTCMobile/ios/ARDSettingsModel.h b/webrtc/examples/objc/AppRTCMobile/ios/ARDSettingsModel.h
index 602a464c8d600bab701fed7ba99b5dc1a5171605..0eb7b31aebbecc1726268c4ea576a97867d28af0 100644
--- a/webrtc/examples/objc/AppRTCMobile/ios/ARDSettingsModel.h
+++ b/webrtc/examples/objc/AppRTCMobile/ios/ARDSettingsModel.h
@@ -49,6 +49,26 @@ NS_ASSUME_NONNULL_BEGIN
 - (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.
  *