Add dummy dart:html library for documentation.

lib/html/doc/interface/SVGLocatable.dart

Index: lib/html/doc/interface/SVGLocatable.dart
diff --git a/lib/html/doc/interface/SVGLocatable.dart b/lib/html/doc/interface/SVGLocatable.dart
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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: Do not edit - generated code.
+
+/// @domName SVGLocatable
+interface SVGLocatable {
+
+  /** @domName SVGLocatable.farthestViewportElement */
+  final SVGElement farthestViewportElement;
+
+  /** @domName SVGLocatable.nearestViewportElement */
+  final SVGElement nearestViewportElement;
+
+  /** @domName SVGLocatable.getBBox */
+  SVGRect getBBox();
+
+  /** @domName SVGLocatable.getCTM */
+  SVGMatrix getCTM();
+
+  /** @domName SVGLocatable.getScreenCTM */
+  SVGMatrix getScreenCTM();
+
+  /** @domName SVGLocatable.getTransformToElement */
+  SVGMatrix getTransformToElement(SVGElement element);
+}