Optimize battery optimize page control flow

- Post the setup logic into background and setup once only when leaving
 this page, this can improve the performance since we won't setup
 every time when switching preference

Bug: 195306545
Bug: 199892006
Test: make SettingsRoboTests
Change-Id: I1c3ee4673cf5cdba0abe39f208dfb1412082c579

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

@@ -74,12 +74,6 @@ public class UnrestrictedPreferenceController extends AbstractPreferenceControll
 
     @Override
     public boolean handlePreferenceTreeClick(Preference preference) {
-        if (!KEY_UNRESTRICTED_PREF.equals(preference.getKey())) {
-            return false;
-        }
-
-        mBatteryOptimizeUtils.setAppOptimizationMode(BatteryOptimizeUtils.MODE_UNRESTRICTED);
-        Log.d(TAG, "Set unrestricted");
-        return true;
+        return getPreferenceKey().equals(preference.getKey());
     }
 }