nixos/tests/chromium: Detect popup using OCR.

This will make the test a lot more reliable, because we no longer need
to press ESC multiple times hoping that it will close the popup.

Unfortunately in order to run this test I needed to locally revert the
gyp update from a305e685

.

With the old gyp version however the test runs fine and it's able to
properly detect the popup.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>