nixos/tests/chromium: Wait 10s after new window

This is a very very very ugly workaround and it's because Chromium seems
to eat keystroke for a few seconds after a new window is created.

I haven't found a better solution yet, so let's at least unbreak the
test until we come up with a better way.

Thanks to @vcunat for bringing this to my attention and also doing the
initial bisect.

The change that brought up this problem was 2b29e401531306d044f797a5dfa,
which updated Chromium from version 65.0.3325.181 to version
66.0.3359.117. Unfortunately the upstream changelog[1] is way too large
to actually guess what the breaking change is.

[1]: https://chromium.googlesource.com/chromium/src/+log/65.0.3325.181..66.0.3359.117?pretty=fuller&n=10000

Signed-off-by: aszlig <aszlig@nix.build>
Cc: @bendlas, @vcunat
(cherry picked from commit 1b1b76f70a9dbf59ad8e833f9de3a60f14cf5471)

nixos/tests/chromium.nix

@@ -94,6 +94,11 @@ mapAttrs (channel: chromiumPkg: makeTest rec {
           ''}");
           if ($status == 0) {
             $ret = 1;
+
+            # XXX: Somehow Chromium is not accepting keystrokes for a few
+            # seconds after a new window has appeared, so let's wait a while.
+            $machine->sleep(10);
+
             last;
           }
           $machine->sleep(1);