Add SearchIndexable to improve search coverage

- Add searachIndex test
- Increase accessibility framework feature fragment coverage

Bug: 197695932
Test: make RunSettingsRoboTests
Change-Id: Icb7e2cf70bb0443304af7866efd48bed1d9af5bf

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

@@ -24,6 +24,7 @@ import static com.google.common.truth.Truth.assertThat;
 import static org.mockito.Mockito.spy;
 import static org.mockito.Mockito.when;
 
+import android.app.settings.SettingsEnums;
 import android.content.Context;
 import android.content.res.Resources;
 import android.os.Bundle;
@@ -70,6 +71,17 @@ public class AccessibilityButtonFragmentTest {
         when(mFragment.getActivity()).thenReturn(Robolectric.setupActivity(FragmentActivity.class));
     }
 
+    @Test
+    public void getMetricsCategory_returnsCorrectCategory() {
+        assertThat(mFragment.getMetricsCategory()).isEqualTo(
+                SettingsEnums.ACCESSIBILITY_BUTTON_SETTINGS);
+    }
+
+    @Test
+    public void getLogTag_returnsCorrectTag() {
+        assertThat(mFragment.getLogTag()).isEqualTo("AccessibilityButtonFragment");
+    }
+
     @Test
     public void onCreate_navigationGestureEnabled_setCorrectTitle() {
         when(mResources.getInteger(com.android.internal.R.integer.config_navBarInteractionMode))