Update API for Objective-C RTCMediaConstraints.

webrtc/api/objc/RTCMediaConstraints.h

Index: webrtc/api/objc/RTCMediaConstraints.h
diff --git a/webrtc/base/objc/NSString+StdString.h b/webrtc/api/objc/RTCMediaConstraints.h
similarity index 56%
copy from webrtc/base/objc/NSString+StdString.h
copy to webrtc/api/objc/RTCMediaConstraints.h
index 8bf6cc94be0346e398ab1a980af6378f06ccb7a5..a8ad39142e39449d75e9b7b40bad09fb2c421124 100644
--- a/webrtc/base/objc/NSString+StdString.h
+++ b/webrtc/api/objc/RTCMediaConstraints.h
@@ -10,16 +10,18 @@
 
 #import <Foundation/Foundation.h>
 
-#include <string>
-
 NS_ASSUME_NONNULL_BEGIN
 
-@interface NSString (StdString)
+@interface RTCMediaConstraints : NSObject
 
-@property(nonatomic, readonly) std::string stdString;
+- (instancetype)init NS_UNAVAILABLE;
 
-+ (std::string)stdStringForString:(NSString *)nsString;
-+ (NSString *)stringForStdString:(const std::string&)stdString;
+/** Initialize with mandatory and/or optional constraints. */
+- (instancetype)initWithMandatoryConstraints:
+    (nullable NSDictionary<NSString *, NSString *> *)mandatory
+                         optionalConstraints:
+    (nullable NSDictionary<NSString *, NSString *> *)optional
+    NS_DESIGNATED_INITIALIZER;
 
 @end