These functions got replaced the the taskrunner API. The new way to
post tasks is as follows:

v8::Platform* platform = ...; // e.g. V8::GetCurrentPlatform();
v8::Isolate* = ...;

std::shared_ptr<v8::TaskRunner> taskrunner = platform->GetForegroundTaskRunner(isolate);
std::unique_ptr<v8::Task> task = ...;

taskrunner->PostTask(std::move(task));

R=ulan@chromium.org

Bug: v8:8238
Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Change-Id: I44a70fc530daae581ee31e54fd09e776ba648406
Reviewed-on: https://chromium-review.googlesource.com/c/1261936Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56400}