Build color_unittests only with flag enabled

Use 'use_color_pipeline' build flag to gate the build and run of
color_unittests.

Since the flag is false by default, remove the unittest from buildbots
for now.

BUG=1003612

Change-Id: Idff6eefb720269e15c60ca69335a5eb0533bd592
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1947225
Reviewed-by: Thomas Lukaszewicz <tluk@chromium.org>
Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Wei Li <weili@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#721264}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 790abd5f4814f10d4070d070de904094a7ddf619
1 file changed