Refactor ActivityStatus to not store current activity

base/android/java/src/org/chromium/base/BaseChromiumApplication.java

Index: base/android/java/src/org/chromium/base/BaseChromiumApplication.java
diff --git a/base/android/java/src/org/chromium/base/BaseChromiumApplication.java b/base/android/java/src/org/chromium/base/BaseChromiumApplication.java
index 97b2ab49a803293c50911add5a6bc8891ea5a650..c921dd9c814ef0449b55c8a41cdbb6346c5e259c 100644
--- a/base/android/java/src/org/chromium/base/BaseChromiumApplication.java
+++ b/base/android/java/src/org/chromium/base/BaseChromiumApplication.java
@@ -4,17 +4,96 @@
 
 package org.chromium.base;
 
+import android.app.Activity;
 import android.app.Application;
+import android.os.Bundle;
+import android.view.Window;
 
 /**
  * Basic application functionality that should be shared among all browser applications.
  */
 public class BaseChromiumApplication extends Application {
+    /**
+     * Interface to be implemented by listeners for window focus events.
+     */
+    public interface WindowFocusChangedListener {
+        /**
+         * Called when the window focus changes for {@code activity}.
+         * @param activity The {@link Activity} that has a window focus changed event.
+         * @param hasFocus Whether or not {@code activity} gained or lost focus.
+         */
+        public void onWindowFocusChanged(Activity activity, boolean hasFocus);
+    }
+
+    private ObserverList<WindowFocusChangedListener> sWindowFocusListeners =
+            new ObserverList<WindowFocusChangedListener>();
 
     @Override
     public void onCreate() {
         super.onCreate();
-        ActivityStatus.initialize(this);
+        ApplicationStatus.initialize(this);
+
+        registerActivityLifecycleCallbacks(new ActivityLifecycleCallbacks() {
+            @Override
+            public void onActivityCreated(final Activity activity, Bundle savedInstanceState) {
+                Window.Callback callback = activity.getWindow().getCallback();
+                activity.getWindow().setCallback(new WindowCallbackWrapper(callback) {
+                    @Override
+                    public void onWindowFocusChanged(boolean hasFocus) {
+                        super.onWindowFocusChanged(hasFocus);
+
+                        for (WindowFocusChangedListener listener : sWindowFocusListeners) {
+                            listener.onWindowFocusChanged(activity, hasFocus);
+                        }
+                    }
+                });
+            }
+
+            @Override
+            public void onActivityDestroyed(Activity activity) {
+                assert activity.getWindow().getCallback() instanceof WindowCallbackWrapper;
+            }
+
+            @Override
+            public void onActivityPaused(Activity activity) {
+                assert activity.getWindow().getCallback() instanceof WindowCallbackWrapper;
+            }
+
+            @Override
+            public void onActivityResumed(Activity activity) {
+                assert activity.getWindow().getCallback() instanceof WindowCallbackWrapper;
+            }
+
+            @Override
+            public void onActivitySaveInstanceState(Activity activity, Bundle outState) {
+                assert activity.getWindow().getCallback() instanceof WindowCallbackWrapper;
+            }
+
+            @Override
+            public void onActivityStarted(Activity activity) {
+                assert activity.getWindow().getCallback() instanceof WindowCallbackWrapper;
+            }
+
+            @Override
+            public void onActivityStopped(Activity activity) {
+                assert activity.getWindow().getCallback() instanceof WindowCallbackWrapper;
+            }
+        });
     }
 
+    /**
+     * Registers a listener to receive window focus updates on activities in this application.
+     * @param listener Listener to receive window focus events.
+     */
+    public void registerWindowFocusChangedListener(WindowFocusChangedListener listener) {
+        sWindowFocusListeners.addObserver(listener);
+    }
+
+    /**
+     * Unregisters a listener from receiving window focus updates on activities in this application.
+     * @param listener Listener that doesn't want to receive window focus events.
+     */
+    public void unregisterWindowFocusChangedListener(WindowFocusChangedListener listener) {
+        sWindowFocusListeners.removeObserver(listener);
+    }
 }