Fix several bugs in closure conversion.

pkg/kernel/lib/transformations/closure/invalidate_closures.dart

Index: pkg/kernel/lib/transformations/closure/invalidate_closures.dart
diff --git a/pkg/kernel/lib/transformations/closure/invalidate_closures.dart b/pkg/kernel/lib/transformations/closure/invalidate_closures.dart
index 96e281e2b1990a992f4c53fb8f42f621aa00bd88..6cbbf76401ac70d983cf024b7c2cb72893ba36fb 100644
--- a/pkg/kernel/lib/transformations/closure/invalidate_closures.dart
+++ b/pkg/kernel/lib/transformations/closure/invalidate_closures.dart
@@ -18,6 +18,7 @@ class InvalidateClosures extends Transformer {
   }
 
   void invalidate(FunctionNode function) {
+    if (function.asyncMarker != AsyncMarker.Sync) return;
     var position = function.location;
     function.body = new ExpressionStatement(new Throw(
         new StringLiteral("Calling unconverted closure at $position")))