Add stop casting button for output switch

This CL add a customize button to stop casting when media
is transferred to info device.

This CL include following change:
- Add new methods to PanelContent.java. Let panels to
  customize "see more button".
- MediaOutputPanel will check which device is used to
  transfer media currently. The customize button will
  shown on when transfer device is info device.
  Then user can use this button to stop casting.
- Add test case.

Bug: 147856563
Test: make -j42 RunSettingsRoboTests
Change-Id: I8b201a10339f39f1d938d99b5659a82014e5bb89

src/com/android/settings/panel/PanelCustomizedButtonCallback.java

@@ -0,0 +1,29 @@
+/*
+ * 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.panel;
+
+/**
+ * PanelCustomizedButtonCallback provides a callback interface for {@link PanelFragment} to receive
+ * events from {@link PanelContent}.
+ */
+public interface PanelCustomizedButtonCallback {
+
+    /**
+     * It will be called when customized button state is changed. For example, custom button
+     * would be hidden for specific behavior.
+     */
+    void onCustomizedButtonStateChanged();
+}