[dart:io] Namespaces for file IO

sdk/lib/io/namespace_impl.dart

Index: sdk/lib/io/namespace_impl.dart
diff --git a/sdk/lib/io/namespace_impl.dart b/sdk/lib/io/namespace_impl.dart
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+// Copyright (c) 2017, 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.
+
+part of dart.io;
+
+// Each Isolate may run in a different "namespace".
+abstract class _Namespace {
+  // This getter does not increase the reference count on the underlying native
+  // object. It cannot be passed in a dispatch message to the IOService thread.
+  external static _Namespace get _namespace;
+
+  // This getter does increase the reference count on the underlying native
+  // object. It must be passed in a dispatch message to the IOService thread.
+  external static int get _namespacePointer;
+
+  // This sets up the Isolate's namespace. It should be set up by the embedder.
+  // If it is not set up by the embedder, relative paths will be resolved
+  // relative to the process's current working directory and absolute paths will
+  // be left relative to the file system root.
+  external static void _setupNamespace(var namespace);
+}