[Extensions] Allow Imprivata extension on the login screen

This CL adds the "Imprivata (login screen)" extension (ID:
lpimkpkllnkdlcigdbgmabfplniahkgm) to the whitelist for extensions on
the login screen.

Bug: 945345
Change-Id: I21b8ad55e77095c144d443741b206a8410a6ab42
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1634692Reviewed-by: Mattias Nissler <mnissler@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Commit-Queue: Alexander Hendrich <hendrich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#672550}

extensions/common/api/_behavior_features.json

@@ -88,7 +88,8 @@
     "platforms": ["chromeos"],
     "whitelist": [
       "FA84F98B32AFC3013F5711F8711F8F38DB210AB7", // Sign-in Screen Test Extension
-      "7FE4A999359A456C4B0FB7B7AD85CEA29CA50519"  // chrome.loginScreenUi Test Extension
+      "7FE4A999359A456C4B0FB7B7AD85CEA29CA50519", // chrome.loginScreenUi Test Extension
+      "E219EE36A3B40612FD2A8CD6937B03EF0C97D3FE"  // Imprivata (login screen)
     ]
   }],
   "allow_deprecated_audio_api": {