Support type variables as expressions.

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

Index: sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart b/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
index 46bece00e25882af8f425bd6c3452d96de5c5024..e94c96459720b2acf6bfa0b6627c3da96bd2ef3a 100644
--- a/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
@@ -1068,6 +1068,12 @@ class JavaScriptBackend extends Backend {
         compiler.listClass, elements);
   }
 
+  void registerTypeVariableExpression(TreeElements elements) {
+    registerRuntimeType(elements);
+    enqueueInResolution(getRuntimeTypeToString(), elements);
+    enqueueInResolution(getCreateRuntimeType(), elements);
+  }
+
   void registerIsCheck(DartType type, Enqueuer world, TreeElements elements) {
     world.registerInstantiatedClass(compiler.boolClass, elements);
     bool isTypeVariable = type.kind == TypeKind.TYPE_VARIABLE;
@@ -1539,6 +1545,10 @@ class JavaScriptBackend extends Backend {
     return compiler.findHelper(const SourceString('getRuntimeTypeArgument'));
   }
 
+  Element getRuntimeTypeToString() {
+    return compiler.findHelper(const SourceString('runtimeTypeToString'));
+  }
+
   Element getCheckArguments() {
     return compiler.findHelper(const SourceString('checkArguments'));
   }