Revert "Do not pause rendering when android activity loses focus (flu…

…tter#4848)" (flutter#4985)

This reverts commit c83d1ef.

lib/ui/window.dart

@@ -47,14 +47,10 @@ enum AppLifecycleState {
   /// in the foreground inactive state. Apps transition to this state when in
   /// a phone call, responding to a TouchID request, when entering the app
   /// switcher or the control center, or when the UIViewController hosting the
-  /// Flutter app is transitioning.
-  ///
-  /// On Android, this corresponds to an app or the Flutter host view running
-  /// in the foreground inactive state.  Apps transition to this state when
-  /// another activity is focused, such as a split-screen app, a phone call,
-  /// a picture-in-picture app, a system dialog, or another window.
-  /// 
-  /// Apps in this state should assume that they may be [paused] at any time.
+  /// Flutter app is transitioning. Apps in this state should assume that they
+  /// may be [paused] at any time.
+  ///
+  /// On Android, this state is currently unused.
   inactive,
 
   /// The application is not currently visible to the user, not responding to

shell/platform/android/io/flutter/app/FlutterActivity.java

@@ -99,12 +99,6 @@ public void onBackPressed() {
             super.onBackPressed();
         }
     }
-
-    @Override
-    protected void onStop() {
-        eventDelegate.onStop();
-        super.onStop();
-    }
 
     @Override
     protected void onPause() {

shell/platform/android/io/flutter/app/FlutterActivityDelegate.java

@@ -218,11 +218,6 @@ public void onResume() {
         }
     }
 
-    @Override
-    public void onStop() {
-        flutterView.onStop();
-    }
-
     @Override
     public void onPostResume() {
         if (flutterView != null) {

shell/platform/android/io/flutter/app/FlutterActivityEvents.java

@@ -54,11 +54,6 @@ public interface FlutterActivityEvents
      */
     void onDestroy();
 
-    /**
-     * @see android.app.Activity#onStop()
-     */
-    void onStop();
-
     /**
      * Invoked when the activity has detected the user's press of the back key.
      *

shell/platform/android/io/flutter/app/FlutterFragmentActivity.java

@@ -98,13 +98,6 @@ public void onBackPressed() {
         }
     }
 
-    @Override
-    protected void onStop() {
-        eventDelegate.onStop();
-        super.onStop();
-    }
-
-
     @Override
     protected void onPause() {
         super.onPause();

shell/platform/android/io/flutter/view/FlutterNativeView.java

@@ -128,14 +128,7 @@ private void attach(FlutterNativeView view) {
 
     // Called by native to send us a platform message.
     private void handlePlatformMessage(final String channel, byte[] message, final int replyId) {
-        // The platform may not be attached immediately in certain cases where a new bundle is run -
-        // the native view is created in a separate thread. This mostly happens when the app restarts in dev
-        // mode when switching into split-screen mode. Preventing app restarts on layout and density
-        // changes will prevent this, and afterwards this can be changed back to an assert.
-        if (!isAttached()) {
-            Log.d(TAG, "PlatformView is not attached");
-            return;
-        }
+        assertAttached();
         BinaryMessageHandler handler = mMessageHandlers.get(channel);
         if (handler != null) {
             try {

shell/platform/android/io/flutter/view/FlutterView.java

@@ -267,7 +267,7 @@ public void addActivityLifecycleListener(ActivityLifecycleListener listener) {
     }
 
     public void onPause() {
-        mFlutterLifecycleChannel.send("AppLifecycleState.inactive");
+        mFlutterLifecycleChannel.send("AppLifecycleState.paused");
     }
 
     public void onPostResume() {
@@ -278,7 +278,7 @@ public void onPostResume() {
     }
 
     public void onStop() {
-        mFlutterLifecycleChannel.send("AppLifecycleState.paused");
+        mFlutterLifecycleChannel.send("AppLifecycleState.suspending");
     }
 
     public void onMemoryPressure() {