Revert "Delete "background process limit" debug option"

This reverts commit c163eb07ce.

Reason for revert: we did a 180 on MCP deprecation, see b/345628418

Change-Id: I2bd2dd7b8fa5275fa81f75d47919ac70d721cd72

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

@@ -0,0 +1,104 @@
+/*
+ * Copyright (C) 2017 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.app.IActivityManager;
+import android.content.Context;
+import android.os.RemoteException;
+
+import androidx.annotation.VisibleForTesting;
+import androidx.preference.ListPreference;
+import androidx.preference.Preference;
+
+import com.android.settings.core.PreferenceControllerMixin;
+import com.android.settingslib.R;
+import com.android.settingslib.development.DeveloperOptionsPreferenceController;
+
+public class BackgroundProcessLimitPreferenceController extends
+        DeveloperOptionsPreferenceController implements Preference.OnPreferenceChangeListener,
+        PreferenceControllerMixin {
+
+    private static final String APP_PROCESS_LIMIT_KEY = "app_process_limit";
+
+    private final String[] mListValues;
+    private final String[] mListSummaries;
+
+    public BackgroundProcessLimitPreferenceController(Context context) {
+        super(context);
+
+        mListValues = context.getResources().getStringArray(R.array.app_process_limit_values);
+        mListSummaries = context.getResources().getStringArray(R.array.app_process_limit_entries);
+    }
+
+    @Override
+    public String getPreferenceKey() {
+        return APP_PROCESS_LIMIT_KEY;
+    }
+
+    @Override
+    public boolean onPreferenceChange(Preference preference, Object newValue) {
+        writeAppProcessLimitOptions(newValue);
+        updateAppProcessLimitOptions();
+        return true;
+    }
+
+    @Override
+    public void updateState(Preference preference) {
+        updateAppProcessLimitOptions();
+    }
+
+    @Override
+    protected void onDeveloperOptionsSwitchDisabled() {
+        super.onDeveloperOptionsSwitchDisabled();
+        writeAppProcessLimitOptions(null);
+    }
+
+    private void updateAppProcessLimitOptions() {
+        try {
+            final int limit = getActivityManagerService().getProcessLimit();
+            int index = 0; // default
+            for (int i = 0; i < mListValues.length; i++) {
+                int val = Integer.parseInt(mListValues[i]);
+                if (val >= limit) {
+                    index = i;
+                    break;
+                }
+            }
+            final ListPreference listPreference = (ListPreference) mPreference;
+            listPreference.setValue(mListValues[index]);
+            listPreference.setSummary(mListSummaries[index]);
+        } catch (RemoteException e) {
+            // intentional no-op
+        }
+    }
+
+    private void writeAppProcessLimitOptions(Object newValue) {
+        try {
+            final int limit = newValue != null ? Integer.parseInt(newValue.toString()) : -1;
+            getActivityManagerService().setProcessLimit(limit);
+            updateAppProcessLimitOptions();
+        } catch (RemoteException e) {
+            // intentional no-op
+        }
+    }
+
+    @VisibleForTesting
+    IActivityManager getActivityManagerService() {
+        return ActivityManager.getService();
+    }
+}

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

@@ -740,6 +740,7 @@ public class DevelopmentSettingsDashboardFragment extends RestrictedDashboardFra
         controllers.add(new StrictModePreferenceController(context));
         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));