Implement subtype for type variables.

sdk/lib/_internal/compiler/implementation/elements/modelx.dart

 // Copyright (c) 2013, 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 elements.modelx;
 
 import 'dart:uri';
 
 import 'elements.dart';
 import '../../compiler.dart' as api;
@@ skipping 1892 matching lines @@
 
   bool get isSwitch => statement is SwitchStatement;
 
   Token position() => statement.getBeginToken();
   String toString() => statement.toString();
 }
 
 class TypeVariableElementX extends ElementX implements TypeVariableElement {
   final Node cachedNode;
   TypeVariableType type;
-  DartType bound;
+  DartType upperBound;
 
   TypeVariableElementX(name, Element enclosing, this.cachedNode,
-                       [this.type, this.bound])
+                       [this.type, this.upperBound])
     : super(name, ElementKind.TYPE_VARIABLE, enclosing);
 
   TypeVariableType computeType(compiler) => type;
 
   Node parseNode(compiler) => cachedNode;
 
   String toString() => "${enclosingElement.toString()}.${name.slowToString()}";
 
   Token position() => cachedNode.getBeginToken();
 }
@@ skipping 42 matching lines @@
 
   MetadataAnnotation ensureResolved(Compiler compiler) {
     if (resolutionState == STATE_NOT_STARTED) {
       compiler.resolver.resolveMetadataAnnotation(this);
     }
     return this;
   }
 
   String toString() => 'MetadataAnnotation($value, $resolutionState)';
 }