Add dummy dart:html library for documentation.

lib/html/doc/interface/SVGLangSpace.dart

Index: lib/html/doc/interface/SVGLangSpace.dart
diff --git a/lib/html/doc/interface/SVGLangSpace.dart b/lib/html/doc/interface/SVGLangSpace.dart
new file mode 100644
index 0000000000000000000000000000000000000000..6c66b1f6c9341894317c8c6fc3c3f7e22df7a3c6
--- /dev/null
+++ b/lib/html/doc/interface/SVGLangSpace.dart
@@ -0,0 +1,15 @@
+// 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 SVGLangSpace
+interface SVGLangSpace {
+
+  /** @domName SVGLangSpace.xmllang */
+  String xmllang;
+
+  /** @domName SVGLangSpace.xmlspace */
+  String xmlspace;
+}