Support type variables as expressions.

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

 // Copyright (c) 2012, 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.
 
 part of dart2js;
 
 /**
  * If true, print a warning for each method that was resolved, but not
  * compiled.
  */
@@ skipping 124 matching lines @@
 
   // The following methods are hooks for the backend to register its
   // helper methods.
   void registerInstantiatedClass(ClassElement cls,
                                  Enqueuer enqueuer,
                                  TreeElements elements) {}
   void registerStringInterpolation(TreeElements elements) {}
   void registerCatchStatement(TreeElements elements) {}
   void registerThrow(TreeElements elements) {}
   void registerLazyField(TreeElements elements) {}
+  void registerTypeVariableExpression(TreeElements elements) {}
   void registerTypeLiteral(TreeElements elements) {}
   void registerStackTraceInCatch(TreeElements elements) {}
   void registerIsCheck(DartType type,
                        Enqueuer enqueuer,
                        TreeElements elements) {}
   void registerAsCheck(DartType type, TreeElements elements) {}
   void registerThrowNoSuchMethod(TreeElements elements) {}
   void registerThrowRuntimeError(TreeElements elements) {}
   void registerAbstractClassInstantiation(TreeElements elements) {}
   void registerFallThroughError(TreeElements elements) {}
@@ skipping 1063 matching lines @@
 
   void close() {}
 
   toString() => name;
 
   /// Convenience method for getting an [api.CompilerOutputProvider].
   static NullSink outputProvider(String name, String extension) {
     return new NullSink('$name.$extension');
   }
 }