anchor.diff:      if (dart.library.js) 'src/webcrypto_impl_js.dart' as impl;
   
   /// Thrown when an operation failed for an operation-specific reason.
  +@sealed
   abstract class OperationError extends Error {
     OperationError._(); // keep the constructor private.
   }
   
   /// A key-pair as returned from key generation.
  +@sealed
   abstract class KeyPair<S, T> {
     KeyPair._(); // keep the constructor private.
   
  
positive.code:   Future<Map<String, dynamic>> exportJsonWebKey();
  }
  
  abstract class AesGcmSecretKey {
    AesGcmSecretKey._(); // keep the constructor private.
  
  
negative.code:   Future<Map<String, dynamic>> exportJsonWebKey();
  }
  
  @sealed
  abstract class HkdfSecretKey {
    HkdfSecretKey._(); // keep the constructor private.
  
  