[PATCH] comctl32/tests: Add test for v6 combobox dropdown size

[Marvin]

Hi,

While running your changed tests on Windows, I think I found new failures.
Being a bot and all I'm not very good at pattern recognition, so I might be
wrong, but could you please double-check?
Full results can be found at
https://testbot.winehq.org/JobDetails.pl?Key=35655

Your paranoid android.


=== wxppro (32 bit combo) ===
combo.c:1279: Test failed: Test 7, expected list height to be 480, got 864

=== w2003std (32 bit combo) ===
combo.c:1279: Test failed: Test 7, expected list height to be 480, got 864