Add dummy dart:html library for documentation.

lib/html/doc/interface/SVGTextPathElement.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 SVGTextPathElement
+interface SVGTextPathElement extends SVGTextContentElement, SVGURIReference {
+
+  static final int TEXTPATH_METHODTYPE_ALIGN = 1;
+
+  static final int TEXTPATH_METHODTYPE_STRETCH = 2;
+
+  static final int TEXTPATH_METHODTYPE_UNKNOWN = 0;
+
+  static final int TEXTPATH_SPACINGTYPE_AUTO = 1;
+
+  static final int TEXTPATH_SPACINGTYPE_EXACT = 2;
+
+  static final int TEXTPATH_SPACINGTYPE_UNKNOWN = 0;
+
+  /** @domName SVGTextPathElement.method */
+  final SVGAnimatedEnumeration method;
+
+  /** @domName SVGTextPathElement.spacing */
+  final SVGAnimatedEnumeration spacing;
+
+  /** @domName SVGTextPathElement.startOffset */
+  final SVGAnimatedLength startOffset;
+}