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

pkg/compiler/lib/src/diagnostics/messages.dart

 // Copyright (c) 2011, 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 messages in this file should meet the following guide lines:
  *
  * 1. The message should be a complete sentence starting with an uppercase
  * letter, and ending with a period.
  *
@@ skipping 308 matching lines @@
   MISSING_FORMALS,
   MISSING_LIBRARY_NAME,
   MISSING_MAIN,
   MISSING_PART_OF_TAG,
   MISSING_TOKEN_AFTER_THIS,
   MISSING_TOKEN_BEFORE_THIS,
   MISSING_TYPE_ARGUMENT,
   MULTI_INHERITANCE,
   NAMED_ARGUMENT_NOT_FOUND,
   NAMED_FUNCTION_EXPRESSION,
-  NAMED_PARAMETER_WITH_EQUALS,
   NATIVE_NOT_SUPPORTED,
   NO_BREAK_TARGET,
   NO_CATCH_NOR_FINALLY,
   NO_COMMON_SUBTYPES,
   NO_CONTINUE_TARGET,
   NO_INSTANCE_AVAILABLE,
   NO_MATCHING_CONSTRUCTOR,
   NO_MATCHING_CONSTRUCTOR_FOR_IMPLICIT,
   NO_STATIC_OVERRIDE,
   NO_STATIC_OVERRIDE_CONT,
@@ skipping 1025 matching lines @@
   foo(a: 1) => print(a);
   foo(2);
 }""",
             """
 main() {
   foo(a = 1) => print(a);
   foo(2);
 }"""
           ]),
 
-      MessageKind.NAMED_PARAMETER_WITH_EQUALS: const MessageTemplate(
-          MessageKind.NAMED_PARAMETER_WITH_EQUALS,
-          "Named optional parameters can't use '=' to specify a default "
-          "value.",
-          howToFix: "Try replacing '=' with ':'.",
-          examples: const [
-            """
-main() {
-  foo({a = 1}) => print(a);
-  foo(a: 2);
-}"""
-          ]),
-
       MessageKind.POSITIONAL_PARAMETER_WITH_EQUALS: const MessageTemplate(
           MessageKind.POSITIONAL_PARAMETER_WITH_EQUALS,
           "Positional optional parameters can't use ':' to specify a "
           "default value.",
           howToFix: "Try replacing ':' with '='.",
           examples: const [
             """
 main() {
   foo([a: 1]) => print(a);
   foo(2);
@@ skipping 2419 matching lines @@
   static String convertToString(value) {
     if (value is ErrorToken) {
       // Shouldn't happen.
       return value.assertionMessage;
     } else if (value is Token) {
       value = value.value;
     }
     return '$value';
   }
 }