Add iOS tracing.

webrtc/base/objc/RTCTracing.h

+/*
+ *  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
+ *  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>
+
+#import "webrtc/base/objc/RTCMacros.h"
+
+RTC_EXPORT void RTCSetupInternalTracer();
+/** Starts capture to specified file. Must be a valid writable path.
+ *  Returns YES if capture starts.
+ */
+RTC_EXPORT BOOL RTCStartInternalCapture(NSString *filePath);
+RTC_EXPORT void RTCStopInternalCapture();
+RTC_EXPORT void RTCShutdownInternalTracer();