Add stats overlay to iOS AppRTCDemo.

webrtc/examples/objc/AppRTCDemo/ARDStatsBuilder.h

+/*
+ *  Copyright 2015 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.
+ */
+
+#import <Foundation/Foundation.h>
+
+@class RTCStatsReport;
+
+/** Class used to accumulate stats information into a single displayable string.
+ */
+@interface ARDStatsBuilder : NSObject
+
+/** String that represents the accumulated stats reports passed into this
+ *  class.
+ */
+@property(nonatomic, readonly) NSString *statsString;
+
+/** Parses the information in the stats report into an appropriate internal
+ *  format used to generate the stats string.
+ */
+- (void)parseStatsReport:(RTCStatsReport *)statsReport;
+
+@end