Add dummy dart:html library for documentation.

lib/html/doc/interface/WebKitCSSFilterValue.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 WebKitCSSFilterValue
+interface WebKitCSSFilterValue extends CSSValueList {
+
+  static final int CSS_FILTER_BLUR = 10;
+
+  static final int CSS_FILTER_BRIGHTNESS = 8;
+
+  static final int CSS_FILTER_CONTRAST = 9;
+
+  static final int CSS_FILTER_CUSTOM = 12;
+
+  static final int CSS_FILTER_DROP_SHADOW = 11;
+
+  static final int CSS_FILTER_GRAYSCALE = 2;
+
+  static final int CSS_FILTER_HUE_ROTATE = 5;
+
+  static final int CSS_FILTER_INVERT = 6;
+
+  static final int CSS_FILTER_OPACITY = 7;
+
+  static final int CSS_FILTER_REFERENCE = 1;
+
+  static final int CSS_FILTER_SATURATE = 4;
+
+  static final int CSS_FILTER_SEPIA = 3;
+
+  /** @domName WebKitCSSFilterValue.operationType */
+  final int operationType;
+}