This is a reland of 92d9b09c.
Patch unchanged, errors fixed by https://crrev.com/c/1430059.

Original change's description:
> [wasm] Decouple background compile jobs from NativeModule
>
> Background compile jobs should not keep the NativeModule alive, for two
> reasons:
> 1) We sometimes have to wait for background compilation to finish (from
>    a foreground task!). This introduces unnecessary latency.
> 2) Giving the background compile tasks shared ownership of the
>    NativeModule causes the NativeModule (and the CompilationState) to
>    be freed from background tasks, which is error-prone (see
>    https://crrev.com/c/1400420).
>
> Instead, this CL introduces a BackgroundCompileToken which is held
> alive by the NativeModule and all background compile jobs. The initial
> and the final phase of compilation (getting and submitting work)
> synchronize on this token to check and ensure that the NativeModule is
> and stays alive. During compilation itself, the mutex is released, such
> that the NativeModule can die.
> The destructor of the NativeModule cancels the BackgroundCompileToken.
> Immediately afterwards, the NativeModule and the CompilationState can
> die.
>
> This change allows to remove two hacks introduced previously: The atomic
> {aborted_} flag and the {FreeCallbacksTask}.
>
> R=mstarzinger@chromium.org
> CC=titzer@chromium.org
>
> Bug: v8:8689, v8:7921
> Change-Id: I42e06eab3c944b0988286f2ce18e3c294535dfb6
> Cq-Include-Trybots: luci.v8.try:v8_linux64_tsan_rel
> Reviewed-on: https://chromium-review.googlesource.com/c/1421364
> Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
> Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#59020}

TBR=mstarzinger@chromium.org

Bug: v8:8689, v8:7921
Change-Id: Iead972ef77c8503da7246cab48e7693b176d8f02
Cq-Include-Trybots: luci.v8.try:v8_linux64_tsan_rel
Reviewed-on: https://chromium-review.googlesource.com/c/1429862Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59035}