Implement the spec's notion of LUB for function types.

pkg/analyzer/lib/src/dart/element/element.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.
 
 library analyzer.src.dart.element.element;
 
 import 'dart:collection';
 import 'dart:math' show min;
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 4086 matching lines @@
    * Initialize a newly created parameter element to have the given [name] and
    * [offset].
    */
   ParameterElementImpl(String name, int nameOffset) : super(name, nameOffset);
 
   /**
    * Initialize a newly created parameter element to have the given [name].
    */
   ParameterElementImpl.forNode(Identifier name) : super.forNode(name);
 
+  /**
+   * Creates a synthetic parameter with [name], [type] and [kind].
+   */
+  factory ParameterElementImpl.synthetic(String name, DartType type,
+      ParameterKind kind) {
+    ParameterElementImpl element = new ParameterElementImpl(name, -1);
+    element.type = type;
+    element.synthetic = true;
+    element.parameterKind = kind;
+    return element;
+  }
+
   @override
   String get defaultValueCode => _defaultValueCode;
 
   /**
    * Set Dart code of the default value.
    */
   void set defaultValueCode(String defaultValueCode) {
     this._defaultValueCode = StringUtilities.intern(defaultValueCode);
   }
 
@@ skipping 639 matching lines @@
 
   @override
   void visitElement(Element element) {
     int offset = element.nameOffset;
     if (offset != -1) {
       map[offset] = element;
     }
     super.visitElement(element);
   }
 }