Add a setting for allowing overlays on Settings app

In the past, we allowed non system overlays on user-debug rom.
Acoording to the user-debug guildline, we should not have differnt
behavior between the user build and user debug rom.

To maintain the consistency between user and user debug rom,
We're creating a new developer setting for allowing non-system overlay on
Settings. By default, we don't allow any non-system app overlays on
Settings app unless user turns it on explictly.

Test: Run robotest. Turn on setting, see the overlays on Settings.
Turn off setting, do not see the overlays on Settings.
Fix: 144989059

Change-Id: I87f00a2eda91de003c6e542e7ec45a066f46fbf7

src/com/android/settings/development/OverlaySettingsPreferenceController.java

@@ -0,0 +1,88 @@
+/*
+ * 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.development;
+
+import android.content.Context;
+import android.content.SharedPreferences;
+
+import androidx.annotation.VisibleForTesting;
+import androidx.preference.Preference;
+import androidx.preference.SwitchPreference;
+
+import com.android.settings.core.PreferenceControllerMixin;
+import com.android.settingslib.development.DeveloperOptionsPreferenceController;
+
+/**
+ * A controller helps enable or disable a developer setting which allows non system overlays on
+ * Settings app.
+ */
+public class OverlaySettingsPreferenceController extends DeveloperOptionsPreferenceController
+        implements Preference.OnPreferenceChangeListener, PreferenceControllerMixin {
+
+    public static final String SHARE_PERFS = "overlay_settings";
+    private static final String KEY_OVERLAY_SETTINGS = "overlay_settings";
+
+    public OverlaySettingsPreferenceController(Context context) {
+        super(context);
+    }
+
+    @Override
+    public boolean isAvailable() {
+        return true;
+    }
+
+    @Override
+    public String getPreferenceKey() {
+        return KEY_OVERLAY_SETTINGS;
+    }
+
+    @Override
+    public boolean onPreferenceChange(Preference preference, Object newValue) {
+        setOverlaySettingsEnabled(mContext, (Boolean) newValue);
+        return true;
+    }
+
+    @Override
+    public void updateState(Preference preference) {
+        ((SwitchPreference) preference).setChecked(isOverlaySettingsEnabled(mContext));
+    }
+
+    /**
+     * Check if this setting is enabled or not.
+     */
+    public static boolean isOverlaySettingsEnabled(Context context) {
+        final SharedPreferences editor = context.getSharedPreferences(SHARE_PERFS,
+                Context.MODE_PRIVATE);
+        return editor.getBoolean(SHARE_PERFS, false /* defValue */);
+    }
+
+    /**
+     * Enable this setting.
+     */
+    @VisibleForTesting
+    static void setOverlaySettingsEnabled(Context context, boolean enabled) {
+        final SharedPreferences editor = context.getSharedPreferences(SHARE_PERFS,
+                Context.MODE_PRIVATE);
+        editor.edit().putBoolean(SHARE_PERFS, enabled).apply();
+    }
+
+    @Override
+    protected void onDeveloperOptionsSwitchDisabled() {
+        super.onDeveloperOptionsSwitchDisabled();
+        setOverlaySettingsEnabled(mContext, false);
+    }
+}