Add dummy dart:html library for documentation.

lib/html/doc/interface/XPathException.dart

Index: lib/html/doc/interface/XPathException.dart
diff --git a/lib/html/doc/interface/XPathException.dart b/lib/html/doc/interface/XPathException.dart
new file mode 100644
index 0000000000000000000000000000000000000000..a8baa7ee7560d10ecaa98190aabd3725ed0fff6c
--- /dev/null
+++ b/lib/html/doc/interface/XPathException.dart
@@ -0,0 +1,25 @@
+// 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: Do not edit - generated code.
+
+/// @domName XPathException
+interface XPathException {
+
+  static final int INVALID_EXPRESSION_ERR = 51;
+
+  static final int TYPE_ERR = 52;
+
+  /** @domName XPathException.code */
+  final int code;
+
+  /** @domName XPathException.message */
+  final String message;
+
+  /** @domName XPathException.name */
+  final String name;
+
+  /** @domName XPathException.toString */
+  String toString();
+}