[Turbofan] Reduce concurrent compilation recursion limit

Renderer hangs are possible with current limit (25). I'd like to know
what a limit of 15 does to benchmark performance, and see it's effect
on hangs.

Bug: chromium:1034768
Change-Id: Ie7fae638972816f547e6ca7a9d7f199cbcf6b2cc
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1981492Reviewed-by: Michael Stanton <mvstanton@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Michael Stanton <mvstanton@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65564}

src/flags/flag-definitions.h

@@ -501,7 +501,7 @@ DEFINE_BOOL(block_concurrent_recompilation, false,
             "block queued jobs until released")
 DEFINE_BOOL(concurrent_inlining, false,
             "run optimizing compiler's inlining phase on a separate thread")
-DEFINE_INT(max_serializer_nesting, 25,
+DEFINE_INT(max_serializer_nesting, 15,
            "maximum levels for nesting child serializers")
 DEFINE_IMPLICATION(future, concurrent_inlining)
 DEFINE_BOOL(trace_heap_broker_verbose, false,