Don't allow non-system window overlays for bug report warnings.

Bug: 175614079
Test: test PoC app
Change-Id: Ie4543c95a6b2d7de47360737b82a6dadde704053

packages/Shell/src/com/android/shell/BugreportWarningActivity.java

@@ -29,6 +29,7 @@ import android.content.Intent;
 import android.os.Build;
 import android.os.Bundle;
 import android.view.LayoutInflater;
+import android.view.WindowManager;
 import android.widget.CheckBox;
 
 import com.android.internal.app.AlertActivity;
@@ -47,6 +48,10 @@ public class BugreportWarningActivity extends AlertActivity
     public void onCreate(Bundle icicle) {
         super.onCreate(icicle);
 
+        // Don't allow overlay windows.
+        getWindow().addSystemFlags(
+                WindowManager.LayoutParams.SYSTEM_FLAG_HIDE_NON_SYSTEM_OVERLAY_WINDOWS);
+
         mSendIntent = getIntent().getParcelableExtra(Intent.EXTRA_INTENT);
 
         // We need to touch the extras to unpack them so they get migrated to