Use RTCAudioSessionDelegate in AudioDeviceIOS.

webrtc/base/objc/RTCMacros.h

Index: webrtc/base/objc/RTCMacros.h
diff --git a/webrtc/base/objc/RTCMacros.h b/webrtc/base/objc/RTCMacros.h
index 9d4646bd2187cfd6990677ae77037bd7b6754a53..71fa0967aca34b7d6d753935b8ef6b0c58fde369 100644
--- a/webrtc/base/objc/RTCMacros.h
+++ b/webrtc/base/objc/RTCMacros.h
@@ -8,8 +8,19 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
+#ifndef WEBRTC_BASE_OBJC_RTC_MACROS_H_
+#define WEBRTC_BASE_OBJC_RTC_MACROS_H_
+
 #if defined(__cplusplus)
-  #define RTC_EXPORT extern "C"
+#define RTC_EXPORT extern "C"
 #else
-  #define RTC_EXPORT extern
+#define RTC_EXPORT extern
 #endif
+
+#ifdef __OBJC__
+#define RTC_FWD_DECL_OBJC_CLASS(classname) @class classname
+#else
+#define RTC_FWD_DECL_OBJC_CLASS(classname) typedef struct objc_object classname
+#endif
+
+#endif // WEBRTC_BASE_OBJC_RTC_MACROS_H_