Chameleon: Force to convert the image to RGB color format

When capturing the screen image from X using import, it may use a
colormap format in order to reduce file size, if the total number of
colors is not too much. However, it makes the image comparison failed
as it is a different format, not RGB. So force to convert it to RGB.

BUG=chromium:397284
TEST=Ran display_Resolution.mirrord on nyan_big passed.

Change-Id: I4ab9494615a52914f49b414f530112a33c4b8f1d
Reviewed-on: https://chromium-review.googlesource.com/292327
Reviewed-by: Yuli Huang <yuli@chromium.org>
Tested-by: Chin-Huang Lin <chinlin@google.com>
Commit-Queue: Chin-Huang Lin <chinlin@google.com>
Trybot-Ready: Chin-Huang Lin <chinlin@google.com>
3 files changed