Generate enum/getters/setters/mappings for word-break.

Currently, the word-break 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 EWordBreak enum and use the generated
CSSValueID <-> EWordBreak mappings.

Diff of generated files:
https://gist.github.com/0d411e2cb2db07f1d076383656211816/revisions

BUG=628043

Review-Url: https://codereview.chromium.org/2898363002
Cr-Commit-Position: refs/heads/master@{#474949}
3 files changed