We can use v8::ArrayBuffer to store struct.

R=dgozman@chromium.org

Bug: none
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I6c4e994e3a8b0a19ad06f89dfadf808f8c6a68e6
Reviewed-on: https://chromium-review.googlesource.com/772036Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49390}