Make `this` available in closures if a type variable is used as expression.

sdk/lib/_internal/compiler/implementation/closure.dart

Index: sdk/lib/_internal/compiler/implementation/closure.dart
diff --git a/sdk/lib/_internal/compiler/implementation/closure.dart b/sdk/lib/_internal/compiler/implementation/closure.dart
index dbfd5b8c6bdec51f25fbbf8d339420c8504a9780..aa17a0079bdad5ed78f786bf586684ab1a367b41 100644
--- a/sdk/lib/_internal/compiler/implementation/closure.dart
+++ b/sdk/lib/_internal/compiler/implementation/closure.dart
@@ -405,6 +405,11 @@ class ClosureTranslator extends Visitor {
   visitIdentifier(Identifier node) {
     if (node.isThis()) {
       useLocal(closureData.thisElement);
+    } else {
+      Element element = elements[node];
+      if (element != null && element.kind == ElementKind.TYPE_VARIABLE) {
+        useLocal(closureData.thisElement);
+      }
     }
     node.visitChildren(this);
   }