Rework type assignability, subtype, and "more specific than" checking.

pkg/analyzer/test/generated/element_test.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.element_test;
 
 import 'package:analyzer/src/generated/ast.dart';
@@ skipping 2615 matching lines @@
     ClassElement classA = ElementFactory.classElement2("A", ["E"]);
     ClassElement classB = ElementFactory.classElement2("B", ["F", "G"]);
     InterfaceTypeImpl typeAF = new InterfaceTypeImpl.con1(classA);
     typeAF.typeArguments = <DartType>[classB.typeParameters[0].type];
     InterfaceTypeImpl typeAG = new InterfaceTypeImpl.con1(classA);
     typeAG.typeArguments = <DartType>[classB.typeParameters[1].type];
     expect(typeAG.isAssignableTo(typeAF), isFalse);
   }
 
   void test_isAssignableTo_void() {
+    InterfaceTypeImpl intType = _typeProvider.intType;
     expect(
-        VoidTypeImpl.instance.isAssignableTo(_typeProvider.intType), isFalse);
+        VoidTypeImpl.instance.isAssignableTo(intType), isFalse);
   }
 
   void test_isDirectSupertypeOf_extends() {
     ClassElement classA = ElementFactory.classElement2("A");
     ClassElement classB = ElementFactory.classElement("B", classA.type);
     InterfaceType typeA = classA.type;
     InterfaceType typeB = classB.type;
     expect(typeA.isDirectSupertypeOf(typeB), isTrue);
   }
 
@@ skipping 1139 matching lines @@
 }
 
 class _FunctionTypeImplTest_isSubtypeOf_baseCase_classFunction
     extends InterfaceTypeImpl {
   _FunctionTypeImplTest_isSubtypeOf_baseCase_classFunction(ClassElement arg0)
       : super.con1(arg0);
 
   @override
   bool get isDartCoreFunction => true;
 }