Use Object::null_instance and Object::null_function and do not create Handles everytime.

runtime/vm/object.h

Index: runtime/vm/object.h
diff --git a/runtime/vm/object.h b/runtime/vm/object.h
index 8d3ef5ed66909c3decd135ee913e2f07ba3a321c..055df48ab06d7886badea92aa89bc162fddcc6fe 100644
--- a/runtime/vm/object.h
+++ b/runtime/vm/object.h
@@ -386,6 +386,10 @@ class Object {
     ASSERT(null_instance_ != NULL);
     return *null_instance_;
   }
+  static const Function& null_function() {
+    ASSERT(null_function_ != NULL);
+    return *null_function_;
+  }
   static const TypeArguments& null_type_arguments() {
     ASSERT(null_type_arguments_ != NULL);
     return *null_type_arguments_;
@@ -787,6 +791,7 @@ class Object {
   static Array* null_array_;
   static String* null_string_;
   static Instance* null_instance_;
+  static Function* null_function_;
   static TypeArguments* null_type_arguments_;
   static Array* empty_array_;
   static Array* zero_array_;