[ios] Add session saving support to clean skeleton.

ios/shared/chrome/browser/ui/browser_list/browser_list_session_service.h

Index: ios/shared/chrome/browser/ui/browser_list/browser_list_session_service.h
diff --git a/ios/shared/chrome/browser/ui/browser_list/browser_list_session_service.h b/ios/shared/chrome/browser/ui/browser_list/browser_list_session_service.h
new file mode 100644
index 0000000000000000000000000000000000000000..3d57fe98988447291b82b70f5bf0db597eec8500
--- /dev/null
+++ b/ios/shared/chrome/browser/ui/browser_list/browser_list_session_service.h
@@ -0,0 +1,33 @@
+// Copyright 2017 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 IOS_SHARED_CHROME_BROWSER_UI_BROWSER_LIST_BROWSER_LIST_SESSION_SERVICE_H_
+#define IOS_SHARED_CHROME_BROWSER_UI_BROWSER_LIST_BROWSER_LIST_SESSION_SERVICE_H_
+
+#include "base/macros.h"
+#include "components/keyed_service/core/keyed_service.h"
+
+// BrowserListSessionService allow saving and restoring saved sessions.
+class BrowserListSessionService : public KeyedService {
+ public:
+  BrowserListSessionService() = default;
+  ~BrowserListSessionService() override = default;
+
+  // Restores the saved session on the current thread. Returns whether the
+  // load was successful or not.
+  virtual bool RestoreSession() = 0;
+
+  // Schedules deletion of the file containing the last session.
+  virtual void ScheduleLastSessionDeletion() = 0;
+
+  // Schedules recording the session on a background thread. If |immediately|
+  // is false, then the session is recorded after a delay. In all case, if a
+  // session recording is scheduled with a delay, it is cancelled.

[rohitrao (ping after 24h), 2017/05/15 11:56:03]

Would it be accurate to switch to this wording? "In all cases, if another
session recording was previously scheduled with a delay, that will be
cancelled."

[sdefresne, 2017/05/15 13:57:36]

Done.

+  virtual void ScheduleSaveSession(bool immediately) = 0;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(BrowserListSessionService);
+};
+
+#endif  // IOS_SHARED_CHROME_BROWSER_UI_BROWSER_LIST_BROWSER_LIST_SESSION_SERVICE_H_