- Implement a first cut for const String.env in the VM to allow

runtime/vm/isolate.h

Index: runtime/vm/isolate.h
===================================================================
--- runtime/vm/isolate.h	(revision 27984)
+++ runtime/vm/isolate.h	(working copy)
@@ -341,6 +341,13 @@
     return init_callback_data_;
   }
 
+  Dart_ConfigCallback config_callback() const {
+    return config_callback_;
+  }
+  void set_config_callback(Dart_ConfigCallback value) {
+    config_callback_ = value;
+  }
+
   Dart_LibraryTagHandler library_tag_handler() const {
     return library_tag_handler_;
   }
@@ -650,6 +657,7 @@
   RawContext* top_context_;
   uword top_exit_frame_info_;
   void* init_callback_data_;
+  Dart_ConfigCallback config_callback_;
   Dart_LibraryTagHandler library_tag_handler_;
   ApiState* api_state_;
   StubCode* stub_code_;