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

webrtc/examples/objc/AppRTCMobile/ios/ARDVideoCallViewController.m

Index: webrtc/examples/objc/AppRTCMobile/ios/ARDVideoCallViewController.m
diff --git a/webrtc/examples/objc/AppRTCMobile/ios/ARDVideoCallViewController.m b/webrtc/examples/objc/AppRTCMobile/ios/ARDVideoCallViewController.m
index aa9ea2113d3ceaaba2b776495eb38cff23f4fcd5..5be92162ad81f350351299b9b8627ecd13a1ed4c 100644
--- a/webrtc/examples/objc/AppRTCMobile/ios/ARDVideoCallViewController.m
+++ b/webrtc/examples/objc/AppRTCMobile/ios/ARDVideoCallViewController.m
@@ -12,12 +12,13 @@
 
 #import "webrtc/modules/audio_device/ios/objc/RTCAudioSession.h"
 
+#import "ARDAppClient.h"
+#import "ARDMediaConstraintsModel.h"
+#import "ARDVideoCallView.h"
 #import "WebRTC/RTCAVFoundationVideoSource.h"
 #import "WebRTC/RTCDispatcher.h"
 #import "WebRTC/RTCLogging.h"
-
-#import "ARDAppClient.h"
-#import "ARDVideoCallView.h"
+#import "WebRTC/RTCMediaConstraints.h"
 
 @interface ARDVideoCallViewController () <ARDAppClientDelegate,
     ARDVideoCallViewDelegate>
@@ -45,6 +46,12 @@
   if (self = [super init]) {
     _delegate = delegate;
     _client = [[ARDAppClient alloc] initWithDelegate:self];
+    ARDMediaConstraintsModel *mediaConstraintsModel = [[ARDMediaConstraintsModel alloc] init];
+    RTCMediaConstraints *defaultMediaStreamConstraints = [[RTCMediaConstraints alloc]
+        initWithMandatoryConstraints:nil
+                 optionalConstraints:[mediaConstraintsModel
+                                         currentMediaConstraintFromStoreAsRTCDictionary]];
+    [_client setDefaultMediaStreamConstraints:defaultMediaStreamConstraints];
     [_client connectToRoomWithId:room
                       isLoopback:isLoopback
                      isAudioOnly:isAudioOnly