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

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

Index: pkg/analysis_server/lib/src/services/completion/dart/utilities.dart
diff --git a/pkg/analysis_server/lib/src/services/completion/dart/utilities.dart b/pkg/analysis_server/lib/src/services/completion/dart/utilities.dart
index a3ec936bb7299bb792ede1bfdfbab7e16b93425f..f64f5d07c1c15dd79c2daecf5dad510f760aab9c 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart/utilities.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart/utilities.dart
@@ -13,6 +13,7 @@ import 'package:analysis_server/src/provisional/completion/dart/completion_dart.
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/standard_ast_factory.dart';
 import 'package:analyzer/dart/ast/token.dart';
+import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/src/dart/ast/token.dart';
 import 'package:analyzer/src/generated/source.dart';
 
@@ -29,6 +30,21 @@ final TypeName NO_RETURN_TYPE = astFactory.typeName(
     null);
 
 /**
+ * Build a default argument list based on the given [requiredParams] and
+ * [namedParams].
+ */
+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.isEmpty ? null : args.join(', ');
+}
+
+/**
  * Create a new protocol Element for inclusion in a completion suggestion.
  */
 protocol.Element createLocalElement(