Add dummy dart:html library for documentation.

lib/html/doc/interface/SVGAngle.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 SVGAngle
+interface SVGAngle {
+
+  static final int SVG_ANGLETYPE_DEG = 2;
+
+  static final int SVG_ANGLETYPE_GRAD = 4;
+
+  static final int SVG_ANGLETYPE_RAD = 3;
+
+  static final int SVG_ANGLETYPE_UNKNOWN = 0;
+
+  static final int SVG_ANGLETYPE_UNSPECIFIED = 1;
+
+  /** @domName SVGAngle.unitType */
+  final int unitType;
+
+  /** @domName SVGAngle.value */
+  num value;
+
+  /** @domName SVGAngle.valueAsString */
+  String valueAsString;
+
+  /** @domName SVGAngle.valueInSpecifiedUnits */
+  num valueInSpecifiedUnits;
+
+  /** @domName SVGAngle.convertToSpecifiedUnits */
+  void convertToSpecifiedUnits(int unitType);
+
+  /** @domName SVGAngle.newValueSpecifiedUnits */
+  void newValueSpecifiedUnits(int unitType, num valueInSpecifiedUnits);
+}