With this cl we start using the custom deleter to free externalized
array buffers. This also allows us to keep wasm memories registered
with the wasm memory tracker and thereby to propagate that a memory
is wasm allocated over postMessage calls.

Bug: v8:8073, chromium:836800
Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Change-Id: I57e3ea44d9c6633ada7996677dd1de4da810ab64
Reviewed-on: https://chromium-review.googlesource.com/1186681Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Stephan Herhut <herhut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55361}