Home default setting should not shown in managed profile settings

Each default preference needs to have its corresponding
PreferenceAvailabilityProvider to provide us the availability of it.
If no corresponding provider is found, it is considered to be not
available. So it encourages other developers who will add new default app
preference later to consider the availability of it.

Bug:27143673
Change-Id: I073b7122dddc579504f397c5de2bdd4df3826269

src/com/android/settings/PreferenceAvailabilityProvider.java

@@ -0,0 +1,30 @@
+/*
+ * Copyright (C) 2016 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;
+
+import android.content.Context;
+
+/**
+ * Interface for classes whose instances can provide the availability of the preference.
+ */
+public interface PreferenceAvailabilityProvider {
+    /**
+     * @return the availability of the preference. Please make sure the availability in managed
+     * profile is taken into account.
+     */
+    boolean isAvailable(Context context);
+}