Pass network config constraint as base64 to avoid mangling bytes

webrtc/sdk/objc/Framework/Classes/NSData+StdString.mm

+/*
+ *  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 "NSData+StdString.h"
+
+@implementation NSData (StdString)
+
+- (std::string)stdString {
+  return [NSData stdStringForData:self];
+}
+
++ (std::string)stdStringForData:(NSData *)nsData {
+  return std::string(reinterpret_cast<const char *>(nsData.bytes),
+                     nsData.length);
+}
+
++ (NSData *)dataForStdString:(const std::string&)stdString {
+  // std::string may contain null termination character so we construct
+  // using length.
+  return [NSData dataWithBytes:stdString.data() length:stdString.length()];
+}
+
+@end