Service isolate rework take 2

runtime/bin/builtin.h

Index: runtime/bin/builtin.h
diff --git a/runtime/bin/builtin.h b/runtime/bin/builtin.h
index 32fde815b61554482fc903454e4cb4ca81c008ed..a943dc853a0c88876ca5487908a25dcde51b2d48 100644
--- a/runtime/bin/builtin.h
+++ b/runtime/bin/builtin.h
@@ -49,6 +49,8 @@ class Builtin {
   // load it.
   static Dart_Handle LoadAndCheckLibrary(BuiltinLibraryId id);
 
+  static void SetLoadPort(Dart_Port port);
+
  private:
   // Map specified URI to an actual file name from 'source_paths' and read
   // the file.
@@ -64,6 +66,7 @@ class Builtin {
   static const char* _builtin_source_paths_[];
   static const char* io_source_paths_[];
   static const char* io_patch_paths_[];
+  static Dart_Port load_port_;
 
   typedef struct {
     const char* url_;