Add dummy dart:html library for documentation.

lib/html/doc/interface/IDBIndex.dart

Index: lib/html/doc/interface/IDBIndex.dart
diff --git a/lib/html/doc/interface/IDBIndex.dart b/lib/html/doc/interface/IDBIndex.dart
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index 0000000000000000000000000000000000000000..55b31b666100ef8665967a202217bde0e292d9a2
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+++ b/lib/html/doc/interface/IDBIndex.dart
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+// 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: Do not edit - generated code.
+
+/// @domName IDBIndex
+interface IDBIndex {
+
+  /** @domName IDBIndex.keyPath */
+  final Dynamic keyPath;
+
+  /** @domName IDBIndex.multiEntry */
+  final bool multiEntry;
+
+  /** @domName IDBIndex.name */
+  final String name;
+
+  /** @domName IDBIndex.objectStore */
+  final IDBObjectStore objectStore;
+
+  /** @domName IDBIndex.unique */
+  final bool unique;
+
+  /** @domName IDBIndex.count */
+  IDBRequest count([key_OR_range]);
+
+  /** @domName IDBIndex.get */
+  IDBRequest get(key);
+
+  /** @domName IDBIndex.getKey */
+  IDBRequest getKey(key);
+
+  /** @domName IDBIndex.openCursor */
+  IDBRequest openCursor([key_OR_range, direction]);
+
+  /** @domName IDBIndex.openKeyCursor */
+  IDBRequest openKeyCursor([key_OR_range, direction]);
+}