Add dummy dart:html library for documentation.

lib/html/doc/interface/FileError.dartdoc

+// 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.
+
+// WARNING:
+//   This file contains documentation that is merged into the real source.
+//   Do not make code changes here.
+
+/// @domName FileError
+interface FileError {
+
+  static final int ABORT_ERR = 3;
+
+  static final int ENCODING_ERR = 5;
+
+  static final int INVALID_MODIFICATION_ERR = 9;
+
+  static final int INVALID_STATE_ERR = 7;
+
+  static final int NOT_FOUND_ERR = 1;
+
+  static final int NOT_READABLE_ERR = 4;
+
+  static final int NO_MODIFICATION_ALLOWED_ERR = 6;
+
+  static final int PATH_EXISTS_ERR = 12;
+
+  static final int QUOTA_EXCEEDED_ERR = 10;
+
+  static final int SECURITY_ERR = 2;
+
+  static final int SYNTAX_ERR = 8;
+
+  static final int TYPE_MISMATCH_ERR = 11;
+
+  /** @domName FileError.code */
+  final int code;
+}