Generate enum/getters/setters/mappings for text-underline-position.

Currently, the text-underline-position 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 TextUnderlinePosition enum and use the generated
CSSValueID <-> TextUnderlinePosition mappings.

Diff of generated files:
https://gist.github.com/660ef70abac1536136fccb33ecf0905a/revisions

Bug: 628043
Change-Id: Ida488dc25572ad5ede5c5f97a7f44a375de4f29b
Reviewed-on: https://chromium-review.googlesource.com/525272
Commit-Queue: Darren Shen <shend@chromium.org>
Reviewed-by: Rune Lillesveen <rune@opera.com>
Reviewed-by: Naina Raisinghani <nainar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#477466}
4 files changed