Worker: Introduce WorkerOptions for module workers

This CL introduces WorkerOptions for module workers. This is not exposed on the
ctor of any workers yet to avoid making developers confused about unimplemented
features.

This also passes the option from DedicatedWorker::Create() to
DedicatedWorkerMessagingProxy::StartWorkerGlobalScope(). Following CLs will
implement the remaining parts and add tests.

This CL doesn't change the existing behavior.

Rough design doc about module workers:
https://docs.google.com/a/chromium.org/document/d/1IMGWAK7Wq37mLehwkbysNRBBnhQBo3z2MbYyMkViEnY/edit?usp=sharing

Bug: 680046
Change-Id: I571e8f540d842bb06878e13d4b383eddc2df42f1
Reviewed-on: https://chromium-review.googlesource.com/813314
Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Commit-Queue: Hiroki Nakagawa <nhiroki@chromium.org>
Cr-Commit-Position: refs/heads/master@{#524377}
9 files changed