This introduces a barrier that ensures that
`V8InspectorClient::runIfWaitingForDebugger()` is only invoked once all
sessions that requested a paused have invoked runIfWaitingForDebugger.
Downstream change: https://chromium-review.googlesource.com/c/chromium/src/+/3977348
Bug: chromium:1352175
Change-Id: I9049c2de6da8e690ad4312cd6cb799619125bb62
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3976353
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Andrey Kosyakov <caseq@chromium.org>
Cr-Commit-Position: refs/heads/main@{#84191}
