Refactor ActivityStatus to not store current activity

base/android/activity_status.cc

-// 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.
-
-#include "base/android/activity_status.h"
-
-#include <jni.h>
-
-#include "base/memory/singleton.h"
-#include "jni/ActivityStatus_jni.h"
-
-namespace base {
-namespace android {
-
-ActivityStatus::Listener::Listener(
-    const ActivityStatus::StateChangeCallback& callback)
-    : callback_(callback) {
-  ActivityStatus::GetInstance()->RegisterListener(this);
-}
-
-ActivityStatus::Listener::~Listener() {
-  ActivityStatus::GetInstance()->UnregisterListener(this);
-}
-
-void ActivityStatus::Listener::Notify(ActivityState state) {
-  callback_.Run(state);
-}
-
-// static
-ActivityStatus* ActivityStatus::GetInstance() {
-  return Singleton<ActivityStatus,
-                   LeakySingletonTraits<ActivityStatus> >::get();
-}
-
-static void OnActivityStateChange(JNIEnv* env, jclass clazz, int new_state) {
-  ActivityStatus* activity_status = ActivityStatus::GetInstance();
-  ActivityState activity_state = static_cast<ActivityState>(new_state);
-  activity_status->OnActivityStateChange(activity_state);
-}
-
-bool ActivityStatus::RegisterBindings(JNIEnv* env) {
-  return RegisterNativesImpl(env);
-}
-
-ActivityStatus::ActivityStatus()
-    : observers_(new ObserverListThreadSafe<Listener>()) {
-  Java_ActivityStatus_registerThreadSafeNativeStateListener(
-      base::android::AttachCurrentThread());
-}
-
-ActivityStatus::~ActivityStatus() {}
-
-void ActivityStatus::RegisterListener(Listener* listener) {
-  observers_->AddObserver(listener);
-}
-
-void ActivityStatus::UnregisterListener(Listener* listener) {
-  observers_->RemoveObserver(listener);
-}
-
-void ActivityStatus::OnActivityStateChange(ActivityState new_state) {
-  observers_->Notify(&ActivityStatus::Listener::Notify, new_state);
-}
-
-}  // namespace android
-}  // namespace base