Add stats overlay to iOS AppRTCDemo.

BUG=
R=jiayl@webrtc.org

Review URL: https://codereview.webrtc.org/1289623005 .

Cr-Commit-Position: refs/heads/master@{#9714}
diff --git a/webrtc/examples/objc/AppRTCDemo/ios/ARDVideoCallViewController.m b/webrtc/examples/objc/AppRTCDemo/ios/ARDVideoCallViewController.m
index 36c0902..a26068f 100644
--- a/webrtc/examples/objc/AppRTCDemo/ios/ARDVideoCallViewController.m
+++ b/webrtc/examples/objc/AppRTCDemo/ios/ARDVideoCallViewController.m
@@ -88,6 +88,12 @@
 }
 
 - (void)appClient:(ARDAppClient *)client
+      didGetStats:(NSArray *)stats {
+  _videoCallView.statsView.stats = stats;
+  [_videoCallView setNeedsLayout];
+}
+
+- (void)appClient:(ARDAppClient *)client
          didError:(NSError *)error {
   NSString *message =
       [NSString stringWithFormat:@"%@", error.localizedDescription];
@@ -107,6 +113,11 @@
   [self switchCamera];
 }
 
+- (void)videoCallViewDidEnableStats:(ARDVideoCallView *)view {
+  _client.shouldGetStats = YES;
+  _videoCallView.statsView.hidden = NO;
+}
+
 #pragma mark - Private
 
 - (void)setLocalVideoTrack:(RTCVideoTrack *)localVideoTrack {