Rename Closure instance field type_arguments_ to instantiator_.

runtime/lib/function.dart

Index: runtime/lib/function.dart
diff --git a/runtime/lib/function.dart b/runtime/lib/function.dart
index 6c1d5ccbd9d5228e8778c1b91d4599b4eaee1618..e5308a4884220e38839bf8e3f00cec1db055ef46 100644
--- a/runtime/lib/function.dart
+++ b/runtime/lib/function.dart
@@ -12,5 +12,14 @@ class _Closure implements Function {
 
   _Closure _clone() native "Closure_clone";
 
-  // The type_arguments_, function_, and context_ fields are not declared here.
+  // No instance fields should be declared before the following 3 fields whose
+  // offsets must be identical in Dart and C++.
+
+  // The following 3 fields are declared both in raw_object.h (for direct access
+  // from C++ code) and also here so that the offset-to-field map used by
+  // deferred objects is properly initialized.
+  // Caution: These fields are not Dart instances, but VM objects.
+  var instantiator_;
+  var function_;
+  var context_;
 }