Generate enum/getters/setters/mappings for text-align-last.

Currently, the text-align-last 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 ETextAlignLast enum and use the generated
CSSValueID <-> ETextAlignLast mappings.

Diff: https://gist.github.com/7ebcc52951f3abdb9e1fd8f23bdb3e71/revisions

BUG=628043

Review-Url: https://codereview.chromium.org/2915543002
Cr-Commit-Position: refs/heads/master@{#475493}
6 files changed