Add dummy dart:html library for documentation.

lib/html/doc/interface/IDBCursor.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 IDBCursor
+interface IDBCursor {
+
+  static final int NEXT = 0;
+
+  static final int NEXT_NO_DUPLICATE = 1;
+
+  static final int PREV = 2;
+
+  static final int PREV_NO_DUPLICATE = 3;
+
+  /** @domName IDBCursor.direction */
+  final String direction;
+
+  /** @domName IDBCursor.key */
+  final Dynamic key;
+
+  /** @domName IDBCursor.primaryKey */
+  final Dynamic primaryKey;
+
+  /** @domName IDBCursor.source */
+  final Dynamic source;
+
+  /** @domName IDBCursor.advance */
+  void advance(int count);
+
+  /** @domName IDBCursor.continueFunction */
+  void continueFunction([/*IDBKey*/ key]);
+
+  /** @domName IDBCursor.delete */
+  IDBRequest delete();
+
+  /** @domName IDBCursor.update */
+  IDBRequest update(/*SerializedScriptValue*/ value);
+}