Cleanup to screensaver settings for O

Reworked the way screensaver settings are laid out for O. Instead of
using the options menu and dialogs to navigate screensaver options,
there are now two rows: one row for the screensaver choice and
optionally its own settings, and one row for the "when to show" setting.
And now there's a nice obvious button you can press to preview your
choices.

Test: 'export ROBOTEST_FILTER="RadioButtonListFragmentTest";\
mmm -j20 packages/apps/Settings/tests/robotests'

Bug: 35031991
Change-Id: Ie7d2055fb45f6dfe72e34cb9598d9a25f7bee75a

src/com/android/settings/dream/StartNowPreferenceController.java

@@ -0,0 +1,66 @@
+/*
+ * 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.dream;
+
+import android.content.Context;
+import android.support.v7.preference.Preference;
+import android.support.v7.preference.PreferenceScreen;
+import android.widget.Button;
+import com.android.settings.R;
+import com.android.settings.applications.LayoutPreference;
+import com.android.settings.core.PreferenceController;
+import com.android.settingslib.dream.DreamBackend;
+
+public class StartNowPreferenceController extends PreferenceController {
+    private static final String TAG = "StartNowPreferenceController";
+    private static final String PREF_KEY = "dream_start_now_button_container";
+    private final DreamBackend mBackend;
+
+    public StartNowPreferenceController(Context context) {
+        super(context);
+
+        mBackend = DreamBackend.getInstance(context);
+    }
+
+    @Override
+    public boolean isAvailable() {
+        return true;
+    }
+
+    @Override
+    public String getPreferenceKey() {
+        return PREF_KEY;
+    }
+
+    @Override
+    public void displayPreference(PreferenceScreen screen) {
+        super.displayPreference(screen);
+
+        LayoutPreference pref = (LayoutPreference) screen.findPreference(getPreferenceKey());
+        Button startButton = (Button)pref.findViewById(R.id.dream_start_now_button);
+        startButton.setOnClickListener(v -> mBackend.startDreaming());
+    }
+
+    @Override
+    public void updateState(Preference preference) {
+        super.updateState(preference);
+
+        Button startButton = (Button)((LayoutPreference)preference)
+                .findViewById(R.id.dream_start_now_button);
+        startButton.setEnabled(mBackend.getWhenToDreamSetting() != DreamBackend.NEVER);
+    }
+}