Refactor least upper bound computation; support bottom correctly.

pkg/analyzer/lib/src/generated/testing/element_factory.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.
 
 // This code was auto-generated, is not intended to be edited, and is subject to
 // significant change. Please see the README file for more information.
 
 library engine.testing.element_factory;
 
 import 'dart:collection';
@@ skipping 538 matching lines @@
       setter.variable = variable;
       setter.parameters =
           <ParameterElement>[requiredParameter2("_$name", type)];
       setter.returnType = VoidTypeImpl.instance;
       setter.type = new FunctionTypeImpl(setter);
       variable.setter = setter;
     }
     return variable;
   }
 
-  static TypeParameterElementImpl typeParameterElement(String name) =>
-      new TypeParameterElementImpl(name, 0);
+  static TypeParameterElementImpl typeParameterElement(String name) {
+    TypeParameterElementImpl element = new TypeParameterElementImpl(name, 0);
+    element.type = new TypeParameterTypeImpl(element);
+    return element;
+  }
 }