Refactor ActivityStatus to not store current activity

base/android/activity_status.h

-// Copyright 2013 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 BASE_ANDROID_ACTIVITY_STATUS_H_
-#define BASE_ANDROID_ACTIVITY_STATUS_H_
-
-#include <jni.h>
-
-#include "base/android/jni_android.h"
-#include "base/base_export.h"
-#include "base/basictypes.h"
-#include "base/memory/ref_counted.h"
-#include "base/memory/singleton.h"
-#include "base/observer_list_threadsafe.h"
-
-namespace base {
-namespace android {
-
-// Define activity state values like ACTIVITY_STATE_CREATED in a
-// way that ensures they're always the same than their Java counterpart.
-enum ActivityState {
-#define DEFINE_ACTIVITY_STATE(x, y) ACTIVITY_STATE_##x = y,
-#include "base/android/activity_state_list.h"
-#undef DEFINE_ACTIVITY_STATE
-};
-
-// A native helper class to listen to state changes of the current
-// Android Activity. This mirrors org.chromium.base.ActivityStatus.
-// any thread.
-//
-// To start listening, create a new instance, passing a callback to a
-// function that takes an ActivityState parameter. To stop listening,
-// simply delete the listener object. The implementation guarantees
-// that the callback will always be called on the thread that created
-// the listener.
-//
-// Example:
-//
-//    void OnActivityStateChange(ActivityState state) {
-//       ...
-//    }
-//
-//    // Start listening.
-//    ActivityStatus::Listener* my_listener =
-//        new ActivityStatus::Listener(base::Bind(&OnActivityStateChange));
-//
-//    ...
-//
-//    // Stop listening.
-//    delete my_listener
-//
-class BASE_EXPORT ActivityStatus {
- public:
-  typedef base::Callback<void(ActivityState)> StateChangeCallback;
-
-  class Listener {
-   public:
-    explicit Listener(const StateChangeCallback& callback);
-    ~Listener();
-
-   private:
-    friend class ActivityStatus;
-
-    void Notify(ActivityState state);
-
-    StateChangeCallback callback_;
-
-    DISALLOW_COPY_AND_ASSIGN(Listener);
-  };
-
-  // NOTE: The Java ActivityStatus is a singleton too.
-  static ActivityStatus* GetInstance();
-
-  // Internal use: must be public to be called from base_jni_registrar.cc
-  static bool RegisterBindings(JNIEnv* env);
-
-  // Internal use only: must be public to be called from JNI and unit tests.
-  void OnActivityStateChange(ActivityState new_state);
-
- private:
-  friend struct DefaultSingletonTraits<ActivityStatus>;
-
-  ActivityStatus();
-  ~ActivityStatus();
-
-  void RegisterListener(Listener* listener);
-  void UnregisterListener(Listener* listener);
-
-  scoped_refptr<ObserverListThreadSafe<Listener> > observers_;
-
-  DISALLOW_COPY_AND_ASSIGN(ActivityStatus);
-};
-
-}  // namespace android
-}  // namespace base
-
-#endif  // BASE_ANDROID_ACTIVITY_STATUS_H_