Clean up demo dir when leaving demo mode

Delete contents of demo dir when device is provisioned and demo_mode is
disabled

Bug: 28855287
Change-Id: I6e1826ec23a2ff92402fe079a9e7b565a2fe04d7
diff --git a/core/java/android/os/Environment.java b/core/java/android/os/Environment.java
index f6e8940..6af0678 100644
--- a/core/java/android/os/Environment.java
+++ b/core/java/android/os/Environment.java
@@ -324,6 +324,33 @@
     }
 
     /**
+     * Return preloads directory.
+     * <p>This directory may contain pre-loaded content such as
+     * {@link #getDataPreloadsDemoDirectory() demo videos} and
+     * {@link #getDataPreloadsAppsDirectory() APK files} .
+     * {@hide}
+     */
+    public static File getDataPreloadsDirectory() {
+        return new File(getDataDirectory(), "preloads");
+    }
+
+    /**
+     * @see #getDataPreloadsDirectory()
+     * {@hide}
+     */
+    public static File getDataPreloadsDemoDirectory() {
+        return new File(getDataPreloadsDirectory(), "demo");
+    }
+
+    /**
+     * @see #getDataPreloadsDirectory()
+     * {@hide}
+     */
+    public static File getDataPreloadsAppsDirectory() {
+        return new File(getDataPreloadsDirectory(), "apps");
+    }
+
+    /**
      * Return the primary shared/external storage directory. This directory may
      * not currently be accessible if it has been mounted by the user on their
      * computer, has been removed from the device, or some other problem has