[ribbon] Merge css_property_base_custom.cc into css_property.cc.

Now that CSSProperty is not generated, we don't need this file.

Note: The functions have been moved without any modification.
Change-Id: I1ab12d34b9df452ecea74a7f977b0719e8bdc892
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1506514
Commit-Queue: Anders Hartvoll Ruud <andruud@chromium.org>
Reviewed-by: Xida Chen <xidachen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#641136}
3 files changed