Trying to re-re-land: Use a PromiseResolver to store reference to Element in getComputedAccessibleNode() implementation.

Bug: 792783
Change-Id: Icdc8423c50eaa051b348c5226af4936e97b39251
Reviewed-on: https://chromium-review.googlesource.com/923141
Commit-Queue: Alice Boxhall <aboxhall@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537568}
15 files changed