Generate getters/setters for Highlight.

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

Diff of generated files:
https://gist.github.com/darrnshn/6568c64622c1f975f9c2124712625460/revisions

BUG=628043

Review-Url: https://codereview.chromium.org/2895133002
Cr-Commit-Position: refs/heads/master@{#475275}
2 files changed