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

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

Index: sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.dart b/sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.dart
index cea45c9df7c59fa73b4f8a1faeacc8c51d9fe3b5..509755f009f588bddcba1901b740e019cc1b2fe1 100644
--- a/sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.dart
@@ -49,6 +49,7 @@ class CodeEmitterTask extends CompilerTask {
   Set<ClassElement> instantiatedClasses;
 
   JavaScriptBackend get backend => compiler.backend;
+  TypeVariableHandler get typeVariableHandler => backend.typeVariableHandler;
 
   String get _ => space;
   String get space => compiler.enableMinification ? "" : " ";
@@ -1621,9 +1622,14 @@ class CodeEmitterTask extends CompilerTask {
   }
 
   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) {