Update API for Objective-C RTCMediaSource.

webrtc/api/objc/RTCMediaSource.h

Index: webrtc/api/objc/RTCMediaSource.h
diff --git a/webrtc/base/objc/NSString+StdString.h b/webrtc/api/objc/RTCMediaSource.h
similarity index 60%
copy from webrtc/base/objc/NSString+StdString.h
copy to webrtc/api/objc/RTCMediaSource.h
index 8bf6cc94be0346e398ab1a980af6378f06ccb7a5..0b36b8d7093543c803f6097d28488efef8678306 100644
--- a/webrtc/base/objc/NSString+StdString.h
+++ b/webrtc/api/objc/RTCMediaSource.h
@@ -10,16 +10,21 @@
 
 #import <Foundation/Foundation.h>
 
-#include <string>
+typedef NS_ENUM(NSInteger, RTCSourceState) {
+  RTCSourceStateInitializing,
+  RTCSourceStateLive,
+  RTCSourceStateEnded,
+  RTCSourceStateMuted,
+};
 
 NS_ASSUME_NONNULL_BEGIN
 
-@interface NSString (StdString)
+@interface RTCMediaSource : NSObject
 
-@property(nonatomic, readonly) std::string stdString;
+/** The current state of the RTCMediaSource. */
+@property(nonatomic, readonly) RTCSourceState state;
 
-+ (std::string)stdStringForString:(NSString *)nsString;
-+ (NSString *)stringForStdString:(const std::string&)stdString;
+- (instancetype)init NS_UNAVAILABLE;
 
 @end