Generate enum/getters/setters/mappings for object-fit and generate getters/setters for object-position.

Currently, the object-fit 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 EObjectFit enum and
use the generated CSSValueID <-> EObjectFit mappings.

Currently, the object-position property is a 'storage_only' field, so
it has no generated public getters/setters. This patch changes it to an
'external' field so that its getters/setters can be generated as well.

Diff: https://gist.github.com/nainar/4f424629173252c98fe47d6b8b5b86af/revisions

BUG=628043

Change-Id: Ibf632aac9ea8d54d2c3f3cf2245dd0b7f2675c03
Reviewed-on: https://chromium-review.googlesource.com/536295
Reviewed-by: Darren Shen <shend@chromium.org>
Commit-Queue: Naina Raisinghani <nainar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#479589}
4 files changed