Add empty Taskbar views and initial TaskbarController

Guarded by a FeatureFlag.

Bug: 171917176
Change-Id: I7145c7ae68282bf53552502798fe758c8c0e285d

quickstep/src/com/android/launcher3/taskbar/TaskbarContainerView.java

@@ -0,0 +1,46 @@
+/*
+ * Copyright (C) 2021 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.launcher3.taskbar;
+
+import android.content.Context;
+import android.util.AttributeSet;
+import android.widget.FrameLayout;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+
+/**
+ * Top-level ViewGroup that hosts the TaskbarView as well as Views created by it such as Folder.
+ */
+public class TaskbarContainerView extends FrameLayout {
+    public TaskbarContainerView(@NonNull Context context) {
+        this(context, null);
+    }
+
+    public TaskbarContainerView(@NonNull Context context, @Nullable AttributeSet attrs) {
+        this(context, attrs, 0);
+    }
+
+    public TaskbarContainerView(@NonNull Context context, @Nullable AttributeSet attrs,
+            int defStyleAttr) {
+        this(context, attrs, defStyleAttr, 0);
+    }
+
+    public TaskbarContainerView(@NonNull Context context, @Nullable AttributeSet attrs,
+            int defStyleAttr, int defStyleRes) {
+        super(context, attrs, defStyleAttr, defStyleRes);
+    }
+}