Add isSliceable API to BasePrefController

Only support explicitly approved Settings Slices,
dictated by controllers which return true for the new
method isSliceable.

Updating the supported settings to a whitelist means that
the method to return all available slices must be updated,
and checking slicability when we index slices.

Test: robotests
Change-Id: I85848c2cdf3e151fa94b33dd1dc5c0374ef94b5b
Merged-In: Ib2b9690cdd0036b5cc4a1cb846c52bce7c824ab9
Fixes: 79779103

src/com/android/settings/display/NightDisplayIntensityPreferenceController.java

@@ -19,6 +19,8 @@ package com.android.settings.display;
 import android.content.Context;
 import android.support.v7.preference.Preference;
 import android.support.v7.preference.PreferenceScreen;
+import android.text.TextUtils;
+
 import com.android.internal.app.ColorDisplayController;
 import com.android.settings.core.SliderPreferenceController;
 import com.android.settings.widget.SeekBarPreference;
@@ -42,6 +44,11 @@ public class NightDisplayIntensityPreferenceController extends SliderPreferenceC
         return AVAILABLE;
     }
 
+    @Override
+    public boolean isSliceable() {
+        return TextUtils.equals(getPreferenceKey(), "night_display_temperature");
+    }
+
     @Override
     public void displayPreference(PreferenceScreen screen) {
         super.displayPreference(screen);