Receiving a broadcast message when home screen is ready.

There is a lag between Pixel/Phone is starting message is displayed and
when the home screen is actually ready. The lag is visible in low-end
devices like JioPhone Next. To solve that a broadcast message is sent
from the QuickstepLauncher class when the UI is ready and the
FallbackHome activity is finished listening to that broadcast message.

Bug: 199120420
Test: Tested on device

Change-Id: Ibc101a249c6dddcb890e8c3b75c9e27858844e9d

src/com/android/settings/FallbackHome.java

@@ -41,6 +41,7 @@ import android.view.animation.AnimationUtils;
 import java.util.Objects;
 
 public class FallbackHome extends Activity {
+    public static final String HOME_IS_READY = "com.android.launcher3.HOME_IS_READY";
     private static final String TAG = "FallbackHome";
     private static final int PROGRESS_TIMEOUT = 2000;
 
@@ -99,7 +100,9 @@ public class FallbackHome extends Activity {
         }
         getWindow().getDecorView().setSystemUiVisibility(flags);
 
-        registerReceiver(mReceiver, new IntentFilter(Intent.ACTION_USER_UNLOCKED));
+        IntentFilter iFilter = new IntentFilter();
+        iFilter.addAction(HOME_IS_READY);
+        registerReceiver(mReceiver, iFilter);
         maybeFinish();
     }