Don't use magic strings/properties to communicate between compiler and runtime.

sdk/lib/_internal/js_runtime/lib/shared/embedded_names.dart

Index: sdk/lib/_internal/js_runtime/lib/shared/embedded_names.dart
diff --git a/sdk/lib/_internal/js_runtime/lib/shared/embedded_names.dart b/sdk/lib/_internal/js_runtime/lib/shared/embedded_names.dart
index 54e7935bc249fb989ff16b90476ab5ce18bca55e..0d53b50901d1b7a068c8978611c7d12ea9f806a5 100644
--- a/sdk/lib/_internal/js_runtime/lib/shared/embedded_names.dart
+++ b/sdk/lib/_internal/js_runtime/lib/shared/embedded_names.dart
@@ -317,8 +317,12 @@ enum JsGetName {
   OPERATOR_AS_PREFIX,
   /// Name used for generated function types on classes and methods.
   SIGNATURE_NAME,
+  /// Name used to store runtime-type information.

[sra1, 2017/02/22 04:23:52]

Name of JavaScript property used to store runtime-type information on instances
of parameterized classes.

[floitsch, 2017/02/22 12:58:06]

Thanks!
done.

+  RTI_NAME,
   /// Name used to tag typedefs.
   TYPEDEF_TAG,
+  /// Name used to tag a function type.
+  FUNCTION_TYPE_TAG,
   /// Name used to tag void return in function type representations in
   /// JavaScript.
   FUNCTION_TYPE_VOID_RETURN_TAG,