Reland http://codereview.chromium.org/4139008, with a different

chrome/browser/extensions/convert_web_app.h

+// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_EXTENSIONS_CONVERT_WEB_APP_H_
+#define CHROME_BROWSER_EXTENSIONS_CONVERT_WEB_APP_H_
+#pragma once
+
+#include <string>
+
+#include "base/ref_counted.h"
+
+class Extension;
+
+namespace base {
+class Time;
+}
+
+namespace webkit_glue {
+struct WebApplicationInfo;
+}
+
+// Generates a version number for an extension from a time. The goal is to make
+// use of the version number to communicate the date in a human readable form,
+// while maintaining high enough resolution to change each time an app is
+// reinstalled. The version that is returned has the format:
+//
+// <year>.<month>.<day>.<fraction>
+//
+// fraction is represented as a number between 0 and 2^16-1. Each unit is
+// ~1.32 seconds.
+std::string ConvertTimeToExtensionVersion(const base::Time& time);
+
+// Wraps the specified web app in an extension. The extension is created
+// unpacked in the system temp dir. Returns a valid extension that the caller
+// should take ownership on success, or NULL and |error| on failure.
+//
+// NOTE: This function does file IO and should not be called on the UI thread.
+// NOTE: The caller takes ownership of the directory at extension->path() on the
+// returned object.
+scoped_refptr<Extension> ConvertWebAppToExtension(
+    const webkit_glue::WebApplicationInfo& web_app_info,
+    const base::Time& create_time);
+
+#endif  // CHROME_BROWSER_EXTENSIONS_CONVERT_WEB_APP_H_