In {WasmEngine::DeleteCompileJobsOnIsolate} (triggered on isolate
teardown), we are deleting the {AsyncCompileJob} with the expectation
that this cancels all background compilation. Since the introduction of
the CompilationState, this is not true any more. The call to
{CompilationState::Abort} is missing.
This CL fixes this by moving the logic from {AsyncCompileJob::Abort} to
{~AsyncCompileJob}, since the former calls the latter anyway.

R=ahaas@chromium.org

Bug: chromium:869420
Change-Id: I4644d161270def0fe3a94d09cde0135ee420a383
Reviewed-on: https://chromium-review.googlesource.com/1172285Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55083}