This ensures exceptions thrown during parsing are properly propagated
into the surrounding {v8::TryCatch} block. Otherwise running more than
one test input in the same Isolate can fail due to pending exceptions. 

R=jochen@chromium.org
BUG=chromium:715037

Change-Id: Iaa5735515dc097d8cb12dcf8672451f3c9503440
Reviewed-on: https://chromium-review.googlesource.com/490047
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45019}