Fixing warnings in public iOS SDK headers.
Building with the newly published cocoapod generated a few warnings,
which looked a bit bad.

Bug: webrtc:8831
Change-Id: I70c06930603b328e4d11c599a5b5dd77b45150c6
Reviewed-on: https://webrtc-review.googlesource.com/46163
Reviewed-by: Anders Carlsson <andersc@webrtc.org>
Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
Commit-Queue: Peter Hanspers <peterhanspers@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21846}
diff --git a/sdk/objc/Framework/Headers/WebRTC/RTCTracing.h b/sdk/objc/Framework/Headers/WebRTC/RTCTracing.h
index 1364791..5e7e48f 100644
--- a/sdk/objc/Framework/Headers/WebRTC/RTCTracing.h
+++ b/sdk/objc/Framework/Headers/WebRTC/RTCTracing.h
@@ -12,10 +12,10 @@
 
 #import <WebRTC/RTCMacros.h>
 
-RTC_EXTERN void RTCSetupInternalTracer();
+RTC_EXTERN void RTCSetupInternalTracer(void);
 /** Starts capture to specified file. Must be a valid writable path.
  *  Returns YES if capture starts.
  */
 RTC_EXTERN BOOL RTCStartInternalCapture(NSString *filePath);
-RTC_EXTERN void RTCStopInternalCapture();
-RTC_EXTERN void RTCShutdownInternalTracer();
+RTC_EXTERN void RTCStopInternalCapture(void);
+RTC_EXTERN void RTCShutdownInternalTracer(void);