Update API for Objective-C RTCStats.

webrtc/api/objc/RTCStatsReport.h

 /*
  *  Copyright 2015 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>
 
 NS_ASSUME_NONNULL_BEGIN
 
-@interface RTCMediaConstraints : NSObject
+/** This does not currently conform to the spec. */
+@interface RTCStatsReport : NSObject
+
+/** Time since 1970-01-01T00:00:00Z in milliseconds. */
+@property(nonatomic, readonly) CFTimeInterval timestamp;
+
+/** The type of stats held by this object. */
+@property(nonatomic, readonly) NSString *type;
+
+/** The identifier for this object. */
+@property(nonatomic, readonly) NSString *statsId;
+
+/** A dictionary holding the actual stats. */
+@property(nonatomic, readonly) NSDictionary<NSString *, NSString *> *values;
 
 - (instancetype)init NS_UNAVAILABLE;
 
-/** Initialize with mandatory and/or optional constraints. */
-- (instancetype)initWithMandatoryConstraints:
-    (nullable NSDictionary<NSString *, NSString *> *)mandatory
-                         optionalConstraints:
-    (nullable NSDictionary<NSString *, NSString *> *)optional
-    NS_DESIGNATED_INITIALIZER;
-
 @end
 
 NS_ASSUME_NONNULL_END