Add empty Taskbar views and initial TaskbarController

Guarded by a FeatureFlag.

Bug: 171917176
Change-Id: I7145c7ae68282bf53552502798fe758c8c0e285d
diff --git a/quickstep/AndroidManifest.xml b/quickstep/AndroidManifest.xml
index 8dab915..d95cc01 100644
--- a/quickstep/AndroidManifest.xml
+++ b/quickstep/AndroidManifest.xml
@@ -32,6 +32,7 @@
     <uses-permission android:name="android.permission.VIBRATE"/>
     <uses-permission android:name="android.permission.QUERY_ALL_PACKAGES"/>
     <uses-permission android:name="${packageName}.permission.HOTSEAT_EDU" />
+    <uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW" />
 
     <application android:backupAgent="com.android.launcher3.LauncherBackupAgent"
          android:fullBackupOnly="true"