Add dummy dart:html library for documentation.

lib/html/doc/interface/SVGPathSegMovetoRel.dart

Index: lib/html/doc/interface/SVGPathSegMovetoRel.dart
diff --git a/lib/html/doc/interface/SVGPathSegMovetoRel.dart b/lib/html/doc/interface/SVGPathSegMovetoRel.dart
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index 0000000000000000000000000000000000000000..af9332e4eab07e1bc336ad5922a61a85dce396d7
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+++ b/lib/html/doc/interface/SVGPathSegMovetoRel.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 SVGPathSegMovetoRel
+interface SVGPathSegMovetoRel extends SVGPathSeg {
+
+  /** @domName SVGPathSegMovetoRel.x */
+  num x;
+
+  /** @domName SVGPathSegMovetoRel.y */
+  num y;
+}