Add dummy dart:html library for documentation.

lib/html/doc/interface/SVGTRefElement.dart

Index: lib/html/doc/interface/SVGTRefElement.dart
diff --git a/lib/html/doc/interface/SVGTRefElement.dart b/lib/html/doc/interface/SVGTRefElement.dart
new file mode 100644
index 0000000000000000000000000000000000000000..e80f39d31e74ba213592b7e3bef4d68b59bb64ac
--- /dev/null
+++ b/lib/html/doc/interface/SVGTRefElement.dart
@@ -0,0 +1,9 @@
+// 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 SVGTRefElement
+interface SVGTRefElement extends SVGTextPositioningElement, SVGURIReference {
+}