Fix serialization of computed style for 'paint-order'

We were always serializing as the completed (all keywords present) form,
which is not the shortest canonical form.

Fold the ComputedStyleUtils helper into the PaintOrder CSSProperty
class, since this is very specific to this property.

Matches WebKit and almost Gecko (which seems to handle some "two
keyword" cases differently.)

Bug: 904898
Change-Id: Ib796a111e601485e339fdf2739a587fb5f893b8a
Commit-Queue: Eric Willigers <>
Reviewed-by: Eric Willigers <>
Reviewed-by: Rune Lillesveen <>
Cr-Commit-Position: refs/heads/master@{#608623}
16 files changed