Tests for `void`.

sdk/lib/_internal/js_runtime/lib/js_helper.dart

Index: sdk/lib/_internal/js_runtime/lib/js_helper.dart
diff --git a/sdk/lib/_internal/js_runtime/lib/js_helper.dart b/sdk/lib/_internal/js_runtime/lib/js_helper.dart
index 86e80d81b6ddbed5229a0da8d4540ac24cdd27c3..34fddfb13f8c020401a2752e85b27bf76fd3741a 100644
--- a/sdk/lib/_internal/js_runtime/lib/js_helper.dart
+++ b/sdk/lib/_internal/js_runtime/lib/js_helper.dart
@@ -163,6 +163,15 @@ bool isNullType(Object type) {
       JS_GET_NAME(JsGetName.NULL_CLASS_TYPE_NAME));
 }
 
+/// Returns true if the given [type] is the `void` type.
+@ForceInline()
+bool isVoidType(Object type) {
+  return JS_BUILTIN('returns:bool;effects:none;depends:none',
+      JsBuiltin.isGivenTypeRti,
+      type,
+      JS_GET_NAME(JsGetName.VOID_CLASS_TYPE_NAME));
+}
+
 /// Returns whether the given type is _the_ Dart Object type.
 // TODO(floitsch): move this to foreign_helper.dart or similar.
 @ForceInline()
@@ -183,6 +192,16 @@ bool isNullTypeRti(type) {
                     JS_GET_NAME(JsGetName.NULL_CLASS_TYPE_NAME));
 }
 
+/// Returns whether the given type is void type.
+// TODO(floitsch): move this to foreign_helper.dart or similar.
+@ForceInline()
+bool isVoidTypeRti(type) {
+  return JS_BUILTIN('returns:bool;effects:none;depends:none',
+      JsBuiltin.isGivenTypeRti,
+      type,
+      JS_GET_NAME(JsGetName.VOID_CLASS_TYPE_NAME));
+}
+
 /// Returns the metadata of the given [index].
 // TODO(floitsch): move this to foreign_helper.dart or similar.
 @ForceInline()
@@ -3698,11 +3717,14 @@ RuntimeType getDynamicRuntimeType() => const DynamicRuntimeType();
 class VoidRuntimeType extends RuntimeType {
   const VoidRuntimeType();
 
-  String toString() => 'void';
+  String toString() => (new Void().runtimeType).toString(); // 'void';
 
   toRti() => throw 'internal error';
 }
 
+/// The internal class representing `void`.
+class Void {}
+
 RuntimeType getVoidRuntimeType() => const VoidRuntimeType();
 
 /**