Add dummy dart:html library for documentation.

lib/html/doc/interface/SVGPatternElement.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 SVGPatternElement
+interface SVGPatternElement extends SVGElement, SVGURIReference, SVGTests, SVGLangSpace, SVGExternalResourcesRequired, SVGStylable, SVGFitToViewBox {
+
+  /** @domName SVGPatternElement.height */
+  final SVGAnimatedLength height;
+
+  /** @domName SVGPatternElement.patternContentUnits */
+  final SVGAnimatedEnumeration patternContentUnits;
+
+  /** @domName SVGPatternElement.patternTransform */
+  final SVGAnimatedTransformList patternTransform;
+
+  /** @domName SVGPatternElement.patternUnits */
+  final SVGAnimatedEnumeration patternUnits;
+
+  /** @domName SVGPatternElement.width */
+  final SVGAnimatedLength width;
+
+  /** @domName SVGPatternElement.x */
+  final SVGAnimatedLength x;
+
+  /** @domName SVGPatternElement.y */
+  final SVGAnimatedLength y;
+}