Implement PrerenderManager::AddPrerenderForOffline()

chrome/browser/prerender/prerender_constants.h

+// Copyright (c) 2016 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_PRERENDER_PRERENDER_CONSTANTS_H_
+#define CHROME_BROWSER_PRERENDER_PRERENDER_CONSTANTS_H_
+
+namespace prerender {
+
+/* Most of the prerender are used in less than 5 minutes. */
+const int kDefaultPrerenderLifeExpectancyMinutes = 5;
+
+/* Offline originated prerenders have an higher life expectancy to have more
+ * time to fully load web pages from slow network before the web content
+ * snapshot. */
+const int kOfflinePrerenderLifeExpectancyMinutes = 20;
+
+}  // namespace prerender
+
+#endif  // CHROME_BROWSER_PRERENDER_PRERENDER_CONSTANTS_H_