Add dummy dart:html library for documentation.

lib/html/doc/interface/SVGDocument.dartdoc

Index: lib/html/doc/interface/SVGDocument.dartdoc
diff --git a/lib/html/doc/interface/SVGDocument.dartdoc b/lib/html/doc/interface/SVGDocument.dartdoc
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index 0000000000000000000000000000000000000000..bb00aa6d860644ae5945b6e454284a1a14a5b0ce
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+++ b/lib/html/doc/interface/SVGDocument.dartdoc
@@ -0,0 +1,17 @@
+// 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 SVGDocument
+interface SVGDocument extends Document {
+
+  /** @domName SVGDocument.rootElement */
+  final SVGSVGElement rootElement;
+
+  /** @domName SVGDocument.createEvent */
+  Event $dom_createEvent(String eventType);
+}