[CompositeAfterPaint] Rewrite some ref tests to avoid subpixel differences

Bug: 524134
Change-Id: I94eec22f0e2724121b040e659323e4170d05555e
Reviewed-on: https://chromium-review.googlesource.com/c/1412995
Reviewed-by: Philip Rogers <pdr@chromium.org>
Reviewed-by: Morten Stenshorne <mstensho@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#623057}
9 files changed