[Security] resolve overlay attack on RequestIgnoreBatteryOptimizations

we should put the addSystemFlags() after onCreate() method rather than the original onStart() method (refer the proposed solution in b/199167909)

Bug: 199167909
Test: make SettingsRoboTests
Change-Id: Ic7361443bfa2e1a6d8d962708c794fa0122a691c

src/com/android/settings/fuelgauge/RequestIgnoreBatteryOptimizations.java

@@ -41,6 +41,8 @@ public class RequestIgnoreBatteryOptimizations extends AlertActivity implements
     @Override
     public void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
+        getWindow().addSystemFlags(android.view.WindowManager.LayoutParams
+                .SYSTEM_FLAG_HIDE_NON_SYSTEM_OVERLAY_WINDOWS);
 
         mPowerWhitelistManager = getSystemService(PowerWhitelistManager.class);
 
@@ -94,13 +96,6 @@ public class RequestIgnoreBatteryOptimizations extends AlertActivity implements
         setupAlert();
     }
 
-    @Override
-    protected void onStart() {
-        super.onStart();
-        getWindow().addSystemFlags(android.view.WindowManager.LayoutParams
-                .SYSTEM_FLAG_HIDE_NON_SYSTEM_OVERLAY_WINDOWS);
-    }
-
     @Override
     public void onClick(DialogInterface dialog, int which) {
         switch (which) {