[CompositeAfterPaint] Rebaseline several tests

- paint/invalidation/compositing/new-stacking-context.html:
    rebaseline png result because of difference of opacity rounding.
    still fails because the text result is not good.
- virtual/scalefactor*/fast/hidpi/static/validation-bubble-apperance-hidpi.html
    rebaseline after we fixed validation bubble for CAP.

Bug: 524134
Change-Id: I3214acebe7cb3a4142811b0b885cde01a419b1a7
Reviewed-on: https://chromium-review.googlesource.com/c/1380234
Reviewed-by: Philip Rogers <pdr@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#617157}
5 files changed