This adds support for exception control flow by adding a counter behind throw
statements (never incremented), as well as a counter for catch and finally
blocks.

Bug: v8:6000
Change-Id: I3959772c889b543ab5e186ad7cd710e55a8aec23
Reviewed-on: https://chromium-review.googlesource.com/558993
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46476}