Chameleon: fix display_HotPlugNoisy.mirrored on link over DP

Link needs time to react to the noise in the mirrored mode. Wait until
the internal resolution changes. If the resolution doesn't change,
we are confident that it is stable. Otherwise, we catch a slow
response.

BUG=chromium:429928
TEST=successfully ran display_HotPlugNoisy.mirrored on link over DP

Change-Id: If19c3cfbc196399de658ab16b37ccc80250edb57
Reviewed-on: https://chromium-review.googlesource.com/262850
Tested-by: Hung-ying Tyan <tyanh@chromium.org>
Reviewed-by: Wai-Hong Tam <waihong@chromium.org>
Commit-Queue: Hung-ying Tyan <tyanh@chromium.org>
1 file changed