[unified-heap] Fix fast/peerconnection/* liveness GC test

Update waitAndGc to call asyncGC function to guarantee that GCs are
indeed run without stack.

Bug: chromium:843903
Change-Id: Id0117fa23f3dbb42f73b521c922a8a2334a1c55e
Reviewed-on: https://chromium-review.googlesource.com/1240302
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#593892}
1 file changed