Add `=` as default-value separator for named parameters.

pkg/analyzer/lib/src/dart/error/syntactic_errors.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /**
  * The errors produced during sytactic analysis (scanning and parsing).
  */
 library analyzer.src.dart.error.syntactic_errors;
 
 import 'package:analyzer/error/error.dart';
@@ skipping 596 matching lines @@
       const ParserErrorCode('UNEXPECTED_TOKEN', "Unexpected token '{0}'");
 
   static const ParserErrorCode WITH_BEFORE_EXTENDS = const ParserErrorCode(
       'WITH_BEFORE_EXTENDS',
       "The extends clause must be before the with clause");
 
   static const ParserErrorCode WITH_WITHOUT_EXTENDS = const ParserErrorCode(
       'WITH_WITHOUT_EXTENDS',
       "The with clause cannot be used without an extends clause");
 
-  static const ParserErrorCode WRONG_SEPARATOR_FOR_NAMED_PARAMETER =
-      const ParserErrorCode('WRONG_SEPARATOR_FOR_NAMED_PARAMETER',
-          "The default value of a named parameter should be preceeded by ':'");
-
   static const ParserErrorCode WRONG_SEPARATOR_FOR_POSITIONAL_PARAMETER =
       const ParserErrorCode('WRONG_SEPARATOR_FOR_POSITIONAL_PARAMETER',
           "The default value of a positional parameter should be preceeded by '='");
 
   static const ParserErrorCode WRONG_TERMINATOR_FOR_PARAMETER_GROUP =
       const ParserErrorCode('WRONG_TERMINATOR_FOR_PARAMETER_GROUP',
           "Expected '{0}' to close parameter group");
 
   static const ParserErrorCode VAR_AND_TYPE = const ParserErrorCode(
       'VAR_AND_TYPE',
@@ skipping 71 matching lines @@
    */
   const ScannerErrorCode(String name, String message, [String correction])
       : super(name, message, correction);
 
   @override
   ErrorSeverity get errorSeverity => ErrorSeverity.ERROR;
 
   @override
   ErrorType get type => ErrorType.SYNTACTIC_ERROR;
 }