Make NinePieceImagePainter tiling setup more functional

Use base::Optional to achieve more "functional" semantics of the helper
functions.

Bug: 614125
Change-Id: Ic3a74ec27d3e05dd59041eee4240c0098c6edd8a
Reviewed-on: https://chromium-review.googlesource.com/c/1456002
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Reviewed-by: Stephen Chenney <schenney@chromium.org>
Cr-Commit-Position: refs/heads/master@{#629628}
1 file changed