Add dummy dart:html library for documentation.

lib/html/doc/interface/SVGFESpotLightElement.dartdoc

+// 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 SVGFESpotLightElement
+interface SVGFESpotLightElement extends SVGElement {
+
+  /** @domName SVGFESpotLightElement.limitingConeAngle */
+  final SVGAnimatedNumber limitingConeAngle;
+
+  /** @domName SVGFESpotLightElement.pointsAtX */
+  final SVGAnimatedNumber pointsAtX;
+
+  /** @domName SVGFESpotLightElement.pointsAtY */
+  final SVGAnimatedNumber pointsAtY;
+
+  /** @domName SVGFESpotLightElement.pointsAtZ */
+  final SVGAnimatedNumber pointsAtZ;
+
+  /** @domName SVGFESpotLightElement.specularExponent */
+  final SVGAnimatedNumber specularExponent;
+
+  /** @domName SVGFESpotLightElement.x */
+  final SVGAnimatedNumber x;
+
+  /** @domName SVGFESpotLightElement.y */
+  final SVGAnimatedNumber y;
+
+  /** @domName SVGFESpotLightElement.z */
+  final SVGAnimatedNumber z;
+}