Pass network config constraint as base64 to avoid mangling bytes

webrtc/sdk/objc/Framework/Headers/WebRTC/RTCMediaConstraints.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.
  */
 
@@ skipping 21 matching lines @@
 
 - (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;
 
+/** Add a new constraint with raw data/bytes. */

[tkchin_webrtc, 2017/02/02 19:04:53]

nit: add a comment like:
Some constraint values require arbitrary bytes instead of a UTF-8 string. In
particular, some constraints take the form of a serialized proto, which is
binary. This is a temporary interface until we determine a better solution.

+- (void)addConstraintForKey:(NSString *)key
+                       data:(NSData *)data
+                isMandatory:(BOOL)isMandatory;
+
 @end
 
 NS_ASSUME_NONNULL_END