Void is not required to be `null` anymore.

pkg/compiler/lib/src/inferrer/type_graph_nodes.dart

Index: pkg/compiler/lib/src/inferrer/type_graph_nodes.dart
diff --git a/pkg/compiler/lib/src/inferrer/type_graph_nodes.dart b/pkg/compiler/lib/src/inferrer/type_graph_nodes.dart
index fa18eb894dbeb9d2c15873575883da926bfa2538..9c315d91a07c9e4a066b76907678843606815a5e 100644
--- a/pkg/compiler/lib/src/inferrer/type_graph_nodes.dart
+++ b/pkg/compiler/lib/src/inferrer/type_graph_nodes.dart
@@ -1732,14 +1732,13 @@ TypeMask _narrowType(
     {bool isNullable: true}) {
   if (annotation.treatAsDynamic) return type;
   if (annotation.isObject) return type;
+  if (annotation.isVoid) return type;
   TypeMask otherType;
   if (annotation.isTypedef || annotation.isFunctionType) {
     otherType = closedWorld.commonMasks.functionType;
   } else if (annotation.isTypeVariable) {
     // TODO(ngeoffray): Narrow to bound.
     return type;
-  } else if (annotation.isVoid) {
-    otherType = closedWorld.commonMasks.nullType;
   } else {
     ResolutionInterfaceType interfaceType = annotation;
     otherType = new TypeMask.nonNullSubtype(interfaceType.element, closedWorld);