Reapply "Add TypeVariable object on runtime to support reflection on type variables." and …

sdk/lib/_internal/compiler/implementation/js_emitter/metadata_emitter.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.
 
 part of dart2js.js_emitter;
 
 class MetadataEmitter extends CodeEmitterHelper {
   /// A list of JS expressions that represent metadata, parameter names and
   /// type, and return types.
   final List<String> globalMetadata = [];
@@ skipping 52 matching lines @@
     if (value == null) {
       compiler.reportInternalError(
           annotation, 'Internal error: value is null');
       return -1;
     }
     return addGlobalMetadata(
         jsAst.prettyPrint(task.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(
+              task.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 47 matching lines @@
       if (link != null) {
         for (; !link.isEmpty; link = link.tail) {
           metadata.add(reifyMetadata(link.head));
         }
       }
       code.body.statements.add(js.string(metadata.join(',')).toStatement());
       return code;
     });
   }
 }