Generate enum/getters/setters/mappings for speak.

Currently, the speak 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 ESpeak enum and use the generated
CSSValueID <-> ESpeak mappings.

Diff of generated files:
https://gist.github.com/aba737ebdcd44f1ee7c05cf332c64324/revisions

BUG=628043

Review-Url: https://codereview.chromium.org/2896723003
Cr-Commit-Position: refs/heads/master@{#474936}
3 files changed