Add turn screen darker fragment in a11y settings text and display

Accessibility settings category restructure, add turn screen darker
fragment for related accessibility services.

Bug: 174829936
Test: atest TurnScreenDarkerFragmentTest, atest AccessibilitySettingsTest
Change-Id: I8aef7a0b5a6d407813aadb22d7ade5103533efa4

tests/robotests/src/com/android/settings/accessibility/TurnScreenDarkerFragmentTest.java

@@ -0,0 +1,50 @@
+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.settings.accessibility;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import android.content.Context;
+
+import androidx.test.core.app.ApplicationProvider;
+
+import com.android.settings.R;
+import com.android.settings.testutils.XmlTestUtils;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.robolectric.RobolectricTestRunner;
+
+import java.util.List;
+
+/** Tests for {@link TurnScreenDarkerFragment}. */
+@RunWith(RobolectricTestRunner.class)
+public class TurnScreenDarkerFragmentTest {
+
+    private Context mContext = ApplicationProvider.getApplicationContext();
+
+    @Test
+    public void getNonIndexableKeys_existInXmlLayout() {
+        final List<String> niks = TurnScreenDarkerFragment.SEARCH_INDEX_DATA_PROVIDER
+                .getNonIndexableKeys(mContext);
+        final List<String> keys =
+                XmlTestUtils.getKeysFromPreferenceXml(mContext,
+                        R.xml.accessibility_turn_screen_darker);
+
+        assertThat(keys).containsAtLeastElementsIn(niks);
+    }
+}