Minor cleanups to use null_array(), null_object() and null_string() handles.

runtime/vm/dart_api_impl.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "include/dart_api.h"
 #include "include/dart_mirrors_api.h"
 #include "include/dart_native_api.h"
 
 #include "platform/assert.h"
 #include "vm/bigint_operations.h"
@@ skipping 3853 matching lines @@
       ? Symbols::Empty()
       : String::Cast(prefix_object);
   if (prefix_vm.IsNull()) {
     RETURN_TYPE_ERROR(isolate, prefix, String);
   }
   CHECK_CALLBACK_STATE(isolate);
 
   const String& prefix_symbol =
       String::Handle(isolate, Symbols::New(prefix_vm));
   const Namespace& import_ns = Namespace::Handle(
-      Namespace::New(import_vm, Array::Handle(), Array::Handle()));
+      Namespace::New(import_vm, Object::null_array(), Object::null_array()));
   if (prefix_vm.Length() == 0) {
     library_vm.AddImport(import_ns);
   } else {
     LibraryPrefix& library_prefix = LibraryPrefix::Handle();
     library_prefix = library_vm.LookupLocalLibraryPrefix(prefix_symbol);
     if (!library_prefix.IsNull()) {
       library_prefix.AddImport(import_ns);
     } else {
       library_prefix = LibraryPrefix::New(prefix_symbol, import_ns);
       library_vm.AddObject(library_prefix, prefix_symbol);
@@ skipping 107 matching lines @@
   }
   {
     NoGCScope no_gc;
     RawObject* raw_obj = obj.raw();
     isolate->heap()->SetPeer(raw_obj, peer);
   }
   return Api::Success();
 }
 
 }  // namespace dart