Expose worklet on Window through attribute renderWorklet.

https://drafts.css-houdini.org/worklets/#dom-window-renderworklet

This may change in the future if HoudiniTF decides to split into separate
Worklets for each stage.

Additionally add kinuko as OWNERS to worklet directory.

BUG=567358

Review URL: https://codereview.chromium.org/1590583002

Cr-Commit-Position: refs/heads/master@{#369778}
6 files changed