Make Telephony related PreferenceController un-sliceable

Since the structure of Telephony is changed, some of Telephony
related PreferenceController cannot be converted to slices
smoothly whether devices have mobile data or not. So we
decided to make them un-sliceable.

Bug: 155846002
Test: robotests, manual
1. Settings -> Settings search -> search for roaming
2. Check that roaming result has no toggle widget.
Change-Id: I7cba8f6a750d9780a59411942665f68dac61248c

src/com/android/settings/network/telephony/TelephonyTogglePreferenceController.java

@@ -59,6 +59,11 @@ public abstract class TelephonyTogglePreferenceController extends TogglePreferen
         mSetSessionCount.getAndDecrement();
     }
 
+    @Override
+    public boolean isSliceable() {
+        return false;
+    }
+
     /**
      * Get carrier config based on specific subscription id.
      *

tests/robotests/src/com/android/settings/network/telephony/TelephonyTogglePreferenceControllerTest.java

@@ -0,0 +1,67 @@
+/*
+ * Copyright (C) 2020 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.network.telephony;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import android.content.Context;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.robolectric.RobolectricTestRunner;
+import org.robolectric.RuntimeEnvironment;
+
+@RunWith(RobolectricTestRunner.class)
+public class TelephonyTogglePreferenceControllerTest {
+
+    private Context mContext;
+    private FakeTelephonyToggle mFakeTelephonyToggle;
+
+    @Before
+    public void setUp() {
+        mContext = RuntimeEnvironment.application;
+        mFakeTelephonyToggle = new FakeTelephonyToggle(mContext, "key");
+    }
+
+    @Test
+    public void isSliceable_byDefault_shouldReturnFalse() {
+        assertThat(mFakeTelephonyToggle.isSliceable()).isFalse();
+    }
+
+    private static class FakeTelephonyToggle extends TelephonyTogglePreferenceController {
+
+        private FakeTelephonyToggle(Context context, String preferenceKey) {
+            super(context, preferenceKey);
+        }
+
+        @Override
+        public boolean isChecked() {
+            return false;
+        }
+
+        @Override
+        public boolean setChecked(boolean isChecked) {
+            return false;
+        }
+
+        @Override
+        public int getAvailabilityStatus(int subId) {
+            return 0;
+        }
+    }
+}