Add dummy dart:html library for documentation.

lib/html/doc/interface/SVGZoomEvent.dartdoc

Index: lib/html/doc/interface/SVGZoomEvent.dartdoc
diff --git a/lib/html/doc/interface/SVGZoomEvent.dartdoc b/lib/html/doc/interface/SVGZoomEvent.dartdoc
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+// 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 SVGZoomEvent
+interface SVGZoomEvent extends UIEvent {
+
+  /** @domName SVGZoomEvent.newScale */
+  final num newScale;
+
+  /** @domName SVGZoomEvent.newTranslate */
+  final SVGPoint newTranslate;
+
+  /** @domName SVGZoomEvent.previousScale */
+  final num previousScale;
+
+  /** @domName SVGZoomEvent.previousTranslate */
+  final SVGPoint previousTranslate;
+
+  /** @domName SVGZoomEvent.zoomRectScreen */
+  final SVGRect zoomRectScreen;
+}