Add DnD as a special case Slice

Add DND Slice as a special case, since there is an existing
inheritance structures in the zen mode preference controllers which
would be too risky to change at this point in the release.

Change-Id: If4b7013be35c89695786af2dbbea2edcf7a189f3
Merged-In: Ice608b9a7bd6f38b73e581eb3723f0a2fae96f2b
Test: make RunSettingsRoboTests
Fixes: 67997377

tests/robotests/src/com/android/settings/wifi/WifiSliceBuilderTest.java

@@ -72,7 +72,6 @@ public class WifiSliceBuilderTest {
         final Slice wifiSlice = WifiSliceBuilder.getSlice(mContext);
         final SliceMetadata metadata = SliceMetadata.from(mContext, wifiSlice);
 
-
         final List<SliceAction> toggles = metadata.getToggles();
         assertThat(toggles).hasSize(1);