ws: EnsureClientHasDrawnWindow sanity check output

Make WindowServerTestImpl::EnsureClientHasDrawnWindow capture
output of the first ClientRoot window of the client and sanity
check the captured pixels. The output is considered okay when
there are more than 5 colors.

Bug: 908545
Change-Id: Iaa2306da6e2b40b0cf9a8379e71f564b0cf92a8b
Reviewed-by: Scott Violet <>
Commit-Queue: Xiyuan Xia <>
Cr-Commit-Position: refs/heads/master@{#622086}
5 files changed