Developer option for the app freezer

The app freezer allows the system to suspend execution for cached apps.
Without it an app can receive CPU time even if cached, so this option
will allow developers to test their code when frozen while their apps
are cached.

The new developer option will present a list of alternatives for the
freezer operating mode:

"device default": use device/system settings to determine whether the
                  freezer is to be enabled or not. This is the current
                  behavior, and default value for the option.
"enabled": force freezer on
"disabled": force freezer off

A dialog prompting the user to reboot is presented upon freezer mode
change. The device is automatically rebooted if the user decides to
proceed.

Bug: 155465196
Change-Id: I857b77cc4fc1ad766e8d5825ada9b271d3e1ab3a
Test: manually verifued the option works as intendend when this patch is
applied with its companion CLs

Change-Id: I26450b7b7ea2b345fd3661d4869fbc74ae38c0c9

res/values/strings.xml

@@ -12051,4 +12051,7 @@
     <string name="no_5g_in_dsds_text" product="device">When using 2 SIMs, this device will be limited to 4G. <annotation id="url">Learn more</annotation>.</string>
     <!-- Help URI, 5G limitation in DSDS condition. [DO NOT TRANSLATE] -->
     <string name="help_uri_5g_dsds" translatable="false"></string>
+
+    <!-- Developer settings: app freezer title [CHAR LIMIT=50]-->
+    <string name="cached_apps_freezer">Suspend execution for cached apps</string>
 </resources>

res/xml/development_settings.xml

@@ -577,6 +577,12 @@
             android:title="@string/show_all_anrs"
             android:summary="@string/show_all_anrs_summary" />
 
+        <ListPreference
+            android:key="cached_apps_freezer"
+            android:title="@string/cached_apps_freezer"
+            android:entries="@array/cached_apps_freezer_entries"
+            android:entryValues="@array/cached_apps_freezer_values" />
+
         <SwitchPreference
             android:key="show_notification_channel_warnings"
             android:title="@string/show_notification_channel_warnings"

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

@@ -0,0 +1,134 @@
+/*
+ * 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.app.ActivityManager;
+import android.content.Context;
+import android.content.DialogInterface;
+import android.os.PowerManager;
+import android.os.RemoteException;
+import android.provider.Settings;
+import android.text.TextUtils;
+import android.util.Log;
+
+import androidx.annotation.VisibleForTesting;
+import androidx.appcompat.app.AlertDialog;
+import androidx.preference.ListPreference;
+import androidx.preference.Preference;
+
+import com.android.settings.R;
+import com.android.settings.core.PreferenceControllerMixin;
+import com.android.settingslib.development.DeveloperOptionsPreferenceController;
+
+
+public class CachedAppsFreezerPreferenceController extends DeveloperOptionsPreferenceController
+        implements Preference.OnPreferenceChangeListener, PreferenceControllerMixin {
+
+    @VisibleForTesting
+    private static final String CACHED_APPS_FREEZER_KEY = "cached_apps_freezer";
+
+    private final String[] mListValues;
+    private final String[] mListSummaries;
+
+    public CachedAppsFreezerPreferenceController(Context context) {
+        super(context);
+
+        mListValues = context.getResources().getStringArray(R.array.cached_apps_freezer_values);
+        mListSummaries = context.getResources().getStringArray(
+                R.array.cached_apps_freezer_entries);
+    }
+
+    @Override
+    public boolean isAvailable() {
+        boolean available = false;
+
+        try {
+            available = ActivityManager.getService().isAppFreezerSupported();
+        } catch (RemoteException e) {
+            Log.w(TAG, "Unable to obtain freezer support status from ActivityManager");
+        }
+
+        return available;
+    }
+
+    @Override
+    public String getPreferenceKey() {
+        return CACHED_APPS_FREEZER_KEY;
+    }
+
+    @Override
+    public boolean onPreferenceChange(Preference preference, Object newValue) {
+        final String currentValue = Settings.Global.getString(mContext.getContentResolver(),
+                Settings.Global.CACHED_APPS_FREEZER_ENABLED);
+
+        if (!newValue.equals(currentValue)) {
+            final AlertDialog dialog = new AlertDialog.Builder(mContext)
+                    .setMessage(R.string.cached_apps_freezer_reboot_dialog_text)
+                    .setPositiveButton(android.R.string.ok, getRebootDialogOkListener(newValue))
+                    .setNegativeButton(android.R.string.cancel, getRebootDialogCancelListener())
+                    .create();
+            dialog.show();
+        }
+
+        return true;
+    }
+
+    private DialogInterface.OnClickListener getRebootDialogOkListener(Object newValue) {
+        return (dialog, which) -> {
+            Settings.Global.putString(mContext.getContentResolver(),
+                    Settings.Global.CACHED_APPS_FREEZER_ENABLED,
+                    newValue.toString());
+
+            updateState(mPreference);
+
+            PowerManager pm = mContext.getSystemService(PowerManager.class);
+            pm.reboot(null);
+        };
+    }
+
+    private DialogInterface.OnClickListener getRebootDialogCancelListener() {
+        return (dialog, which) -> {
+            updateState(mPreference);
+        };
+    }
+
+    @Override
+    public void updateState(Preference preference) {
+        final ListPreference listPreference = (ListPreference) preference;
+        final String currentValue = Settings.Global.getString(mContext.getContentResolver(),
+                Settings.Global.CACHED_APPS_FREEZER_ENABLED);
+
+        int index = 0; // Defaults to device default
+        for (int i = 0; i < mListValues.length; i++) {
+            if (TextUtils.equals(currentValue, mListValues[i])) {
+                index = i;
+                break;
+            }
+        }
+
+        listPreference.setValue(mListValues[index]);
+        listPreference.setSummary(mListSummaries[index]);
+    }
+
+    @Override
+    public void onDeveloperOptionsDisabled() {
+        super.onDeveloperOptionsDisabled();
+
+        Settings.Global.putString(mContext.getContentResolver(),
+                Settings.Global.CACHED_APPS_FREEZER_ENABLED,
+                mListValues[0].toString());
+    }
+}

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

@@ -499,6 +499,7 @@ public class DevelopmentSettingsDashboardFragment extends RestrictedDashboardFra
         controllers.add(new ProfileGpuRenderingPreferenceController(context));
         controllers.add(new KeepActivitiesPreferenceController(context));
         controllers.add(new BackgroundProcessLimitPreferenceController(context));
+        controllers.add(new CachedAppsFreezerPreferenceController(context));
         controllers.add(new ShowFirstCrashDialogPreferenceController(context));
         controllers.add(new AppsNotRespondingPreferenceController(context));
         controllers.add(new NotificationChannelWarningsPreferenceController(context));