Use StyleImage::HasIntrinsicSize in FillLayer invalidation determination

This better matches what BackgroundImageGeometry checks.

Rename the somewhat terse |img| to the ever so slightly less terse
|image|, and mark it const.

Change-Id: I9e3cbe86285bc448c2e79d31c813071191150a11
Reviewed-on: https://chromium-review.googlesource.com/c/1489235
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Commit-Queue: Stephen Chenney <schenney@chromium.org>
Auto-Submit: Fredrik Söderquist <fs@opera.com>
Reviewed-by: Stephen Chenney <schenney@chromium.org>
Cr-Commit-Position: refs/heads/master@{#635566}
1 file changed