Add display settings dashboard to new IA.

- Added a activity-alias pointing to displaySettings as top level
  setting item.
- Refactored all preference logic in DisplaySettings into
  PreferenceControllers. During fragment onAttach it installs all
  controllers, and during onResume it updates preference state. Each
  controller listens to its own preference change event.

Bug: 31800242
Test: RunSettingsRoboTests
Change-Id: Ibc9bf200c5acce7c4ae9292340822afee27a3a28

src/com/android/settings/display/ScreenSaverPreferenceController.java

@@ -0,0 +1,55 @@
+/*
+ * 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.display;
+
+import android.content.Context;
+import android.support.v7.preference.Preference;
+import android.support.v7.preference.PreferenceScreen;
+
+import com.android.settings.DreamSettings;
+import com.android.settings.core.PreferenceController;
+
+public class ScreenSaverPreferenceController extends PreferenceController {
+
+    private static final String KEY_SCREEN_SAVER = "screensaver";
+
+    public ScreenSaverPreferenceController(Context context) {
+        super(context);
+    }
+
+    @Override
+    protected boolean isAvailable() {
+        return mContext.getResources().getBoolean(
+                com.android.internal.R.bool.config_dreamsSupported);
+    }
+
+    @Override
+    protected String getPreferenceKey() {
+        return KEY_SCREEN_SAVER;
+    }
+
+    @Override
+    public boolean handlePreferenceTreeClick(Preference preference) {
+        return false;
+    }
+
+    @Override
+    public void updateState(PreferenceScreen screen) {
+        final Preference preference = screen.findPreference(KEY_SCREEN_SAVER);
+        if (preference != null) {
+            preference.setSummary(
+                    DreamSettings.getSummaryTextWithDreamName(mContext));
+        }
+    }
+}