Worklet: Introduce WorkletOptions for addModule()

This CL introduces WorkletOptions dictionary for addModule(). This provides
"RequestCredentials" option, but it's not actually used yet because module
loading part is still under development. Once the module loading is enabled,
we'll add layout tests for this option.

Spec: https://drafts.css-houdini.org/worklets/#dictdef-workletoptions

BUG=710837
TBR=ikilpatrick@chromium.org

Review-Url: https://codereview.chromium.org/2868413005
Cr-Commit-Position: refs/heads/master@{#471296}
15 files changed