Add dummy dart:html library for documentation.

lib/html/doc/interface/FileException.dartdoc

Index: lib/html/doc/interface/FileException.dartdoc
diff --git a/lib/html/doc/interface/FileException.dartdoc b/lib/html/doc/interface/FileException.dartdoc
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+++ b/lib/html/doc/interface/FileException.dartdoc
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+// 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 FileException
+interface FileException {
+
+  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 FileException.code */
+  final int code;
+
+  /** @domName FileException.message */
+  final String message;
+
+  /** @domName FileException.name */
+  final String name;
+
+  /** @domName FileException.toString */
+  String toString();
+}