Add iOS tracing.

webrtc/base/objc/RTCTracing.h

Index: webrtc/base/objc/RTCTracing.h
diff --git a/webrtc/examples/objc/AppRTCDemo/ARDTURNClient.h b/webrtc/base/objc/RTCTracing.h
similarity index 51%
copy from webrtc/examples/objc/AppRTCDemo/ARDTURNClient.h
copy to webrtc/base/objc/RTCTracing.h
index 8f2a81734229fca65421613794b3ab1accca8c2e..5c0dc01b09c4f9a134e7fa23c0649e767775ce5e 100644
--- a/webrtc/examples/objc/AppRTCDemo/ARDTURNClient.h
+++ b/webrtc/base/objc/RTCTracing.h
@@ -1,5 +1,5 @@
 /*
- *  Copyright 2014 The WebRTC Project Authors. All rights reserved.
+ *  Copyright 2016 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
@@ -10,11 +10,10 @@
 
 #import <Foundation/Foundation.h>
 
-@protocol ARDTURNClient <NSObject>
+#import "webrtc/base/objc/RTCMacros.h"
 
-// Returns TURN server urls if successful.
-- (void)requestServersWithCompletionHandler:
-    (void (^)(NSArray *turnServers,
-              NSError *error))completionHandler;
-
-@end
+RTC_EXPORT void RTCSetupInternalTracer();
+/** Starts capture to specified file. Must be a valid writable path. */

[Chuck, 2016/02/02 16:32:50]

Can you add what happens if it isn't to the comment?

+RTC_EXPORT BOOL RTCStartInternalCapture(NSString *filePath);
+RTC_EXPORT void RTCStopInternalCapture();
+RTC_EXPORT void RTCShutdownInternalTracer();