Allows IndicatorView to have a different size than Settings Activity

The transparent IndicatorView need to be immersive fullscreen, while the
underneath activity should not cover the status bar or the nav bar.

Bug: 157747505
Test: Manual test to verify status bar and nav bar are visible.
Change-Id: I6d5a3f53dd3768524700c3e33135fa7dfde839f1

AndroidManifest.xml

@@ -103,6 +103,7 @@
     <uses-permission android:name="android.permission.MEDIA_CONTENT_CONTROL" />
     <uses-permission android:name="android.permission.INSTALL_DYNAMIC_SYSTEM" />
     <uses-permission android:name="android.permission.BIND_CELL_BROADCAST_SERVICE" />
+    <uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW" />
     
     <application android:label="@string/settings_label"
             android:icon="@drawable/ic_launcher_settings"

src/com/android/settings/gestures/BackGestureIndicatorView.java

@@ -92,9 +92,7 @@ public class BackGestureIndicatorView extends LinearLayout {
         int copiedFlags = (parentWindowAttributes.flags
                 & WindowManager.LayoutParams.FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS);
         final WindowManager.LayoutParams lp = new WindowManager.LayoutParams(
-                ViewGroup.LayoutParams.MATCH_PARENT,
-                ViewGroup.LayoutParams.MATCH_PARENT,
-                WindowManager.LayoutParams.TYPE_APPLICATION,
+                WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY,
                 WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED
                         | WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE
                         | WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE