Update API for Objective-C RTCAudioTrack and RTCVideoTrack.

webrtc/api/objc/RTCAudioTrack.h

Index: webrtc/api/objc/RTCAudioTrack.h
diff --git a/webrtc/api/objc/RTCVideoSource.h b/webrtc/api/objc/RTCAudioTrack.h
similarity index 61%
copy from webrtc/api/objc/RTCVideoSource.h
copy to webrtc/api/objc/RTCAudioTrack.h
index a98fa6c6bba626c52ea4331bb1b3d4d6bd0bd1a9..76036ccec88921ee6af373891b22fa40bc7ed21c 100644
--- a/webrtc/api/objc/RTCVideoSource.h
+++ b/webrtc/api/objc/RTCAudioTrack.h
@@ -8,24 +8,20 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-#import <Foundation/Foundation.h>
-
-typedef NS_ENUM(NSInteger, RTCSourceState) {
-  RTCSourceStateInitializing,
-  RTCSourceStateLive,
-  RTCSourceStateEnded,
-  RTCSourceStateMuted,
-};
+#import "RTCMediaStreamTrack.h"
 
 NS_ASSUME_NONNULL_BEGIN
 
-@interface RTCVideoSource : NSObject
+@class RTCPeerConnectionFactory;
 
-/** The current state of the RTCVideoSource. */
-@property(nonatomic, readonly) RTCSourceState state;
+@interface RTCAudioTrack : RTCMediaStreamTrack
 
 - (instancetype)init NS_UNAVAILABLE;
 
+/** Initialize an RTCAudioTrack with an id. */
+- (instancetype)initWithFactory:(RTCPeerConnectionFactory *)factory
+                        trackId:(NSString *)trackId;
+
 @end
 
 NS_ASSUME_NONNULL_END