move polymer.dart into dart svn

pkg/polymer/lib/src/file_system.dart

+// Copyright (c) 2012, 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.
+
+/** Abstraction for file systems and utility functions to manipulate paths. */
+library file_system;
+
+import 'dart:async';
+
+/**
+ * Abstraction around file system access to work in a variety of different
+ * environments.
+ */
+abstract class FileSystem {
+  /**
+   * Apply all pending writes.  Until this method is called, writeString is not
+   * guaranteed to have any observable impact.
+   */
+  Future flush();
+
+  /**
+   * Reads bytes if possible, but falls back to text if running in a browser.
+   * Return type is either [Future<List<int>>] or [Future<String>].
+   */
+  Future readTextOrBytes(String path);
+
+  /* Like [readTextOrBytes], but decodes bytes as UTF-8. Used for Dart code. */
+  Future<String> readText(String path);
+
+  /**
+   * Writes [text] to file at [path]. Call flush to insure that changes are
+   * visible.
+   */
+  void writeString(String path, String text);
+}