GCC may be buggy in how it handles visibility in this case. The
previous nested implementation resulted in a 'lambda1 declared with
greater visibility than the type of its field lambda2' error.

Unnesting the inner lambda works around the error.

Bug: v8:8126
Change-Id: Id822ca80fec9af27c4adc7ff53be3b6d9478f0d7
Reviewed-on: https://chromium-review.googlesource.com/1206310Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55638}