Default arg support continued (flutter-intellij#553).

pkg/analysis_server/lib/src/services/completion/dart/local_reference_contributor.dart

 // Copyright (c) 2015, 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.
 
 library services.completion.contributor.dart.local_ref;
 
 import 'dart:async';
 
 import 'package:analysis_server/plugin/protocol/protocol.dart' as protocol
     show Element, ElementKind;
@@ skipping 464 matching lines @@
         .where((FormalParameter param) => param.kind == ParameterKind.REQUIRED)
         .map((p) => p.element);
     suggestion.requiredParameterCount = requiredParameters.length;
 
     Iterable<ParameterElement> namedParameters = paramList
         .where((FormalParameter param) => param.kind == ParameterKind.NAMED)
         .map((p) => p.element);
     suggestion.hasNamedParameters = namedParameters.isNotEmpty;
 
     suggestion.defaultArgumentListString =
-        _buildDefaultArgList(requiredParameters, namedParameters);
-  }
-
-  String _buildDefaultArgList(Iterable<ParameterElement> requiredParams,
-      Iterable<ParameterElement> namedParams) {
-    List<String> args = requiredParams.map((p) => p.name).toList();
-    List<String> requiredArgs = namedParams
-        .where((p) => p.isRequired)
-        .map((p) => '${p.name}: null')
-        .toList();
-    args.addAll(requiredArgs);
-    return args.join(', ');
+        buildDefaultArgList(requiredParameters, namedParameters);
   }
 
   bool _isVoid(TypeAnnotation returnType) {
     if (returnType is TypeName) {
       Identifier id = returnType.name;
       if (id != null && id.name == 'void') {
         return true;
       }
     }
     return false;
@@ skipping 17 matching lines @@
       String text = documentationComment.tokens
           .map((Token t) => t.toString())
           .join('\n')
           .replaceAll('\r\n', '\n');
       String doc = removeDartDocDelimiters(text);
       suggestion.docComplete = doc;
       suggestion.docSummary = getDartDocSummary(doc);
     }
   }
 }