Add dummy dart:html library for documentation.

lib/html/doc/interface/ElementTimeControl.dart

+// 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 ElementTimeControl
+interface ElementTimeControl {
+
+  /** @domName ElementTimeControl.beginElement */
+  void beginElement();
+
+  /** @domName ElementTimeControl.beginElementAt */
+  void beginElementAt(num offset);
+
+  /** @domName ElementTimeControl.endElement */
+  void endElement();
+
+  /** @domName ElementTimeControl.endElementAt */
+  void endElementAt(num offset);
+}