Tests for `void`.

sdk/lib/_internal/js_runtime/lib/js_rti.dart

Index: sdk/lib/_internal/js_runtime/lib/js_rti.dart
diff --git a/sdk/lib/_internal/js_runtime/lib/js_rti.dart b/sdk/lib/_internal/js_runtime/lib/js_rti.dart
index de7db233558002a16e2375aa284c7530a769bb20..29a1d85a4df403c1607bb11bbe63adc989e7a7b8 100644
--- a/sdk/lib/_internal/js_runtime/lib/js_rti.dart
+++ b/sdk/lib/_internal/js_runtime/lib/js_rti.dart
@@ -164,6 +164,9 @@ String runtimeTypeToString(var rti, {String onTypeVariable(int i)}) {
     // A list representing a type with arguments.
     return getRuntimeTypeAsString(rti, onTypeVariable: onTypeVariable);
   }
+  if (isVoidTypeRti(rti)) {
+    return "void";
+  }
   if (isJsFunction(rti)) {
     // A reference to the constructor.
     return rawRtiToJsConstructorName(rti);