Generate enum/getters/setters for transform-style.

Currently, the transform-style (named TransformStyle3D internally)
property is a 'storage_only' field, so it has no generated public
getters/setters.

This patch changes it to a 'keyword' field so that its getters/setters
can be generated as well. We also generate the ETransformStyle3D enum.
Although there are generated CSSValueID <-> ETransformStyle3D mappings,
they are not used because the handwritten code don't have them.

Diff: https://gist.github.com/nainar/56e680b491980fcb82332c616ab47c65/revisions

Bug: 628043
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: I95ffd60c4edcc155b1b58a87f8f9380a22bc8b18
Reviewed-on: https://chromium-review.googlesource.com/536222
Reviewed-by: Darren Shen <shend@chromium.org>
Reviewed-by: meade_UTC10 <meade@chromium.org>
Commit-Queue: nainar <nainar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#479984}
9 files changed