cros: Whitelist autotest_private_ext in public sessions

The Autotest component extension is used to launch Android apps. It
should be whitelisted in Demo Mode (which is implemented as public
sessions).

Bug: 870049
Change-Id: I31628dc5c659818990c1d280d6744112867db34a
Reviewed-on: https://chromium-review.googlesource.com/c/1441795Reviewed-by: Ivan Šandrk <isandrk@chromium.org>
Reviewed-by: Achuith Bhandarkar <achuith@chromium.org>
Commit-Queue: Wenzhao (Colin) Zang <wzang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#630498}

extensions/browser/device_local_account_util.cc

@@ -111,6 +111,7 @@ const char* const kPublicSessionWhitelist[] = {
     "ilnpadgckeacioehlommkaafedibdeob",  // Enterprise DeviceAttributes
     "oflckobdemeldmjddmlbaiaookhhcngo",  // Citrix Receiver QA version
     "ljacajndfccfgnfohlgkdphmbnpkjflk",  // Chrome Remote Desktop (Dev Build)
+    "behllobkkfkfnphdnhnkndlbkcpglgmj",  // Autotest
 
     // Google Apps:
     "mclkkofklkfljcocdinagocijmpgbhab",  // Google input tools