Add TypeVariable object on runtime to support reflection on type variables.

sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.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.js_emitter;
 
 /**
  * Generates the code for all used classes in the program. Static fields (even
  * in classes) are ignored, since they can be treated as non-class elements.
  *
@@ skipping 31 matching lines @@
   /// type, and return types.
   final List<String> globalMetadata = [];
 
   /// A map used to canonicalize the entries of globalMetadata.
   final Map<String, int> globalMetadataMap = <String, int>{};
 
   // TODO(ngeoffray): remove this field.
   Set<ClassElement> instantiatedClasses;
 
   JavaScriptBackend get backend => compiler.backend;
+  TypeVariableHandler get typeVariableHandler => backend.typeVariableHandler;
 
   String get _ => space;
   String get space => compiler.enableMinification ? "" : " ";
   String get n => compiler.enableMinification ? "" : "\n";
   String get N => compiler.enableMinification ? "\n" : ";\n";
 
   /**
    * List of expressions and statements that will be included in the
    * precompiled function.
    *
@@ skipping 1552 matching lines @@
     if (value == null) {
       compiler.reportInternalError(
           annotation, 'Internal error: value is null');
       return -1;
     }
     return addGlobalMetadata(
         jsAst.prettyPrint(constantReference(value), compiler).getText());
   }
 
   int reifyType(DartType type) {
-    // TODO(ahe): Handle type variables correctly instead of using "#".
-    String representation = backend.rti.getTypeRepresentation(type, (_) {});
-    return addGlobalMetadata(representation.replaceAll('#', 'null'));
+    jsAst.Expression representation =
+        backend.rti.getTypeRepresentation(type, (variable) {
+          return js.toExpression(
+              typeVariableHandler.reifyTypeVariable(variable.element));
+        });
+
+    return addGlobalMetadata(
+        jsAst.prettyPrint(representation, compiler).getText());
   }
 
   int reifyName(SourceString name) {
     return addGlobalMetadata('"${name.slowToString()}"');
   }
 
   int addGlobalMetadata(String string) {
     return globalMetadataMap.putIfAbsent(string, () {
       globalMetadata.add(string);
       return globalMetadata.length - 1;
@@ skipping 509 matching lines @@
     return compiler.deferredLoadTask.isDeferred(element);
   }
 
   bool get areAnyElementsDeferred {
     return compiler.deferredLoadTask.areAnyElementsDeferred;
   }
 }
 
 // TODO(ahe): Move code for interceptors to own file.
 // TODO(ahe): Move code for reifying metadata/types to own file.