iOS - Add iceRegatherIntervalRange.

webrtc/sdk/objc/Framework/Headers/WebRTC/RTCIntervalRange.h

+/*
+ *  Copyright 2017 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 RTCIntervalRange : NSObject
+
+@property(nonatomic, readonly) NSInteger min;
+@property(nonatomic, readonly) NSInteger max;
+
+- (instancetype)init;
+- (instancetype)initWithMin:(NSInteger)min
+                        max:(NSInteger)max
+    NS_DESIGNATED_INITIALIZER;
+
+@end
+
+NS_ASSUME_NONNULL_END
+