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}

webrtc/examples/objc/AppRTCDemo/ios/ARDVideoCallView.h

@@ -12,6 +12,8 @@
 
 #import "RTCEAGLVideoView.h"
 
+#import "ARDStatsView.h"
+
 @class ARDVideoCallView;
 @protocol ARDVideoCallViewDelegate <NSObject>
 
@@ -21,6 +23,9 @@
 // Called when the hangup button is pressed.
 - (void)videoCallViewDidHangup:(ARDVideoCallView *)view;
 
+// Called when stats are enabled by triple tapping.
+- (void)videoCallViewDidEnableStats:(ARDVideoCallView *)view;
+
 @end
 
 // Video call view that shows local and remote video, provides a label to
@@ -30,6 +35,7 @@
 @property(nonatomic, readonly) UILabel *statusLabel;
 @property(nonatomic, readonly) RTCEAGLVideoView *localVideoView;
 @property(nonatomic, readonly) RTCEAGLVideoView *remoteVideoView;
+@property(nonatomic, readonly) ARDStatsView *statsView;
 @property(nonatomic, weak) id<ARDVideoCallViewDelegate> delegate;
 
 @end