Create a separate microtask queue for the LayoutWorkletGlobalScope.

As above, this unblocks:
https://chromium-review.googlesource.com/c/chromium/src/+/1716035/13

Which requires a separate microtask queue for the CSS Layout API.

Bug: 726125
Change-Id: Ib7f5cc158e0aa53b9bca0b8e70c73dcc551c1e05
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1738007
Commit-Queue: Yuta Kitamura <yutak@chromium.org>
Reviewed-by: Yuta Kitamura <yutak@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#684717}
5 files changed