Implement automatic loading of dart:core_native_fields library

vm/object_store.h

Index: vm/object_store.h
===================================================================
--- vm/object_store.h	(revision 1545)
+++ vm/object_store.h	(working copy)
@@ -191,6 +191,11 @@
     core_impl_library_ = value.raw();
   }
 
+  RawLibrary* native_fields_library() const { return native_fields_library_; }
+  void set_native_fields_library(const Library& value) {
+    native_fields_library_ = value.raw();
+  }
+
   RawLibrary* root_library() const { return root_library_; }
   void set_root_library(const Library& value) {
     root_library_ = value.raw();
@@ -273,6 +278,7 @@
   RawArray* symbol_table_;
   RawLibrary* core_library_;
   RawLibrary* core_impl_library_;
+  RawLibrary* native_fields_library_;
   RawLibrary* root_library_;
   RawLibrary* registered_libraries_;
   RawArray* pending_classes_;