Compile rtc_api_objc on Mac.

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
+// TODO(hjon): Update nullability types. See http://crbug/webrtc/5592
 
 /** 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;
+@property(nonatomic, readonly) NSDictionary *values;
+// @property(nonatomic, readonly) NSDictionary<NSString *, NSString *> *values;
 
 - (instancetype)init NS_UNAVAILABLE;
 
 @end
 
 NS_ASSUME_NONNULL_END