The new API receives a unique_ptr to avoid leaking the Extension object.
All chromium uses were refactored in https://crrev.com/c/1447652.

R=adamk@chromium.org

Bug: v8:8725
Cq-Include-Trybots: luci.chromium.try:linux-blink-rel
Change-Id: I46a931a73e941fe7b78f5390fec74663677e13e4
Reviewed-on: https://chromium-review.googlesource.com/c/1454723Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59451}