Add dummy dart:html library for documentation.

lib/html/doc/nodoc-src/_IDBKeyRangeFactoryProvider.dart

+// 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.
+
+class _IDBKeyRangeFactoryProvider {
+
+  factory IDBKeyRange.only(/*IDBKey*/ value) => null;
+
+  factory IDBKeyRange.lowerBound(/*IDBKey*/ bound, [bool open = false]) => null;
+
+  factory IDBKeyRange.upperBound(/*IDBKey*/ bound, [bool open = false]) => null;
+
+  factory IDBKeyRange.bound(/*IDBKey*/ lower, /*IDBKey*/ upper,
+                            [bool lowerOpen = false, bool upperOpen = false]) =>
+      null;
+}