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 86329e0a106b35b669cdbc2c34d642e98e1b29d4..640bf52d34f2fdc711b967a867b40d74e9aef22d 100644
--- a/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
@@ -1028,6 +1028,12 @@ class JavaScriptBackend extends Backend {
     compiler.enqueuer.resolution.registerInstantiatedClass(compiler.listClass);
   }
 
+  void registerTypeVariable() {
+    registerRuntimeType();
+    enqueueInResolution(getRuntimeTypeToString());
+    enqueueInResolution(getCreateRuntimeType());
+  }
+
   void registerIsCheck(DartType type, Enqueuer world) {
     bool isTypeVariable = type.kind == TypeKind.TYPE_VARIABLE;
     if (!type.isRaw || isTypeVariable) {
@@ -1487,6 +1493,10 @@ 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'));
   }