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This reverts commit 02090026.

Reason for revert: Causing crashes in canary.

Original change's description:
> [Reland] webaudio: Always delete handlers in a non-nestable task on the main thread.
>
> Deleting handlers does considerable non-trivial work that requires the
> graph lock. Allowing this to happen during finalization introduces
> considerable complexity because it can happen during any GC heap allocation,
> including ones that occur while the graph lock is already held.
>
> Instead, when the last reference is dropped, the handler is not deleted
> immediately, but a non-nestable task to delete it is enqueued. Since the
> task is non-nestable, it will not run while the graph lock is held by the
> main thread (and if it is held by another thread, it will block on it).
>
> This slightly extends the lifetime of audio handlers, during which time
> it is illegal to take a new reference (and RefCounted checks this in
> debug builds). So a flag is set in the destructor (though it could be
> sensibly set as early as the ref count reaches zero) that prevents the
> handler from adding itself to the tail processing queue if it is already
> being destroyed.
>
> The cycle collection layout test is updated to handle the fact that the
> handler count does not go to zero immediately on GC, but shortly thereafter.
> This has been done by merging with another recently added unit test, which
> tests something very similar (a cycle of one element).
>
> The leak detector has been augmented to wait for audio handlers that are
> awaiting deletion, if there are any.
>
> Bug: 884059
> Change-Id: I818bcdbf87dc3e83359ad7a62aa56547dea2d7a5
> Reviewed-on: https://chromium-review.googlesource.com/c/1392109
> Reviewed-by: Kentaro Hara <haraken@chromium.org>
> Reviewed-by: Hongchan Choi <hongchan@chromium.org>
> Commit-Queue: Jeremy Roman <jbroman@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#621840}

TBR=jbroman@chromium.org,haraken@chromium.org,hongchan@chromium.org

Change-Id: Ib13b613f6fa696935f64362f65eb94cba50acdfd
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 884059,921018
Reviewed-on: https://chromium-review.googlesource.com/c/1407501
Commit-Queue: Jeremy Roman <jbroman@chromium.org>
Reviewed-by: Jeremy Roman <jbroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#622109}