Make the dart:mojo.internal import configuration specific.

mojo/dart/packages/mojo/lib/src/handle.dart

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 part of core;
 
 class MojoHandle {
+  // TODO(floitsch): get the INVALID value from the backing internal
+  // implementation.
   static const int INVALID = 0;
   static const int DEADLINE_INDEFINITE = -1;
 
-  int _h;
-  int get h => _h;
+  // The type of this field is determined by the backing internal
+  // implementation.
+  Object _h;
+  Object get h => _h;
 
   MojoHandle(this._h, {String description}) {
     MojoHandleNatives.addOpenHandle(_h, description: description);
   }
 
   MojoHandle._internal(this._h);
 
   MojoHandle.invalid() : this._internal(INVALID);
 
   int close() {
@@ skipping 59 matching lines @@
   }
 
   static bool registerFinalizer(MojoEventSubscription eventSubscription) {
     return MojoHandleNatives.registerFinalizer(
             eventSubscription, eventSubscription._handle.h) ==
         MojoResult.kOk;
   }
 
   static bool reportLeakedHandles() => MojoHandleNatives.reportOpenHandles();
 }