Introduce lock_screen_apps to chrome/browser/chromeos

chrome/browser/chromeos/lock_screen_apps/state_controller.h

+// 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 CHROME_BROWSER_CHROMEOS_LOCK_SCREEN_APPS_STATE_CONTROLLER_H_
+#define CHROME_BROWSER_CHROMEOS_LOCK_SCREEN_APPS_STATE_CONTROLLER_H_
+
+#include "base/lazy_instance.h"
+#include "base/observer_list.h"
+#include "chrome/browser/chromeos/lock_screen_apps/state_observer.h"
+#include "chrome/browser/chromeos/lock_screen_apps/types.h"
+
+namespace lock_screen_apps {
+class StateObserver;

[xiyuan, 2017/05/02 18:12:23]

nit: move this down after line 17. Prevailing style leverage's existing
namespace for forward decls.

[tbarzic, 2017/05/02 18:43:37]

Done.

+}
+
+namespace lock_screen_apps {
+
+// Manages state of lock scree action handler apps, and notifies
+// interested parties as the state changes.
+// Currently assumes single supported action - NEW_NOTE.
+class StateController {
+ public:
+  static StateController* Get();
+
+  void AddObserver(StateObserver* observer);
+  void RemoveObserver(StateObserver* observer);
+
+  // Gets current state assiciated with the action.
+  ActionState GetActionState(Action action) const;
+
+  // Handles an action request - if the action handler is available, this will
+  // show an app window for the specified action.
+  void HandleAction(Action action);

[xiyuan, 2017/05/02 18:12:23]

Do we care about whether the action is handled? e.g. return a bool to indicate
that.

[tbarzic, 2017/05/02 18:43:37]

Not necessarily, but it could be useful, e.g. for tests. 

+
+  // If there are any active lock screen action handlers, moved their windows
+  // to background, to ensure lock screen UI is visible.
+  void MoveToBackground();
+
+ private:
+  friend struct base::LazyInstanceTraitsBase<StateController>;
+
+  StateController();
+  ~StateController();
+
+  // Requests action state change to |state|.
+  // Returns whether the action state has changed.
+  bool UpdateActionState(Action action, ActionState state);

[xiyuan, 2017/05/02 18:12:23]

How do we plan to change state with this method being private? By HandleAction()
?

[tbarzic, 2017/05/02 18:43:37]

Yes, I plan not to have this expose explicit update state method. Instead it
will expose specific actions (like HandleAction, or MoveToBackground, observers
for session state (to disable actions on user unlock, to track state of
registered apps)) that will internally update the state.

[xiyuan, 2017/05/02 19:23:03]

Acknowledged.

+
+  // notifies observers that an action state changed.
+  void NotifyStateChanged(Action action);
+
+  // New note action state.
+  ActionState new_note_state_ = ActionState::kNotSupported;
+
+  base::ObserverList<StateObserver> observers_;
+
+  DISALLOW_COPY_AND_ASSIGN(StateController);
+};
+
+}  // namespace lock_screen_apps
+
+#endif  // CHROME_BROWSER_CHROMEOS_LOCK_SCREEN_APPS_STATE_CONTROLLER_H_