Add dummy dart:html library for documentation.

lib/html/doc/interface/XPathException.dartdoc

Index: lib/html/doc/interface/XPathException.dartdoc
diff --git a/lib/html/doc/interface/XPathException.dartdoc b/lib/html/doc/interface/XPathException.dartdoc
new file mode 100644
index 0000000000000000000000000000000000000000..4ee9b7b9a18fa1412701553a072682dc4f4e0e57
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+++ b/lib/html/doc/interface/XPathException.dartdoc
@@ -0,0 +1,27 @@
+// 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 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();
+}