We need to throw before rethrowing, otherwise the exception does
not trigger a debugger event and is not reported if uncaught.

R=gsathya@chromium.org, jgruber@chromium.org

Bug: v8:7047
Change-Id: I7ce0253883a21d6059e4e0ed0fc56dc55a0dcba6
Reviewed-on: https://chromium-review.googlesource.com/758372Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49237}