DevTools: catch FormatterWorker acorn errors
DevTools: catch FormatterWorker acorn errors

Calling `acorn.parse()` in FormattedWorker may throw an error. If we
do not catch it, the error may appear in layout test results, making
tests flaky, such as
http/tests/devtools/console/console-correct-suggestions.js

This CL always catches errors from acorn.parse().

Bug: none
Change-Id: Ief452572c04ea45ae9a930999441e799e8f73f7d
Reviewed-on: https://chromium-review.googlesource.com/1159231
Reviewed-by: Andrey Lushnikov <73889f071ff743ad62763f13ff61c52ca3ee19d0@chromium.org>
Reviewed-by: Joel Einbinder <bab755abe9fee48fe544272e55f73517d4e4a725@chromium.org>
Commit-Queue: Erik Luo <26192f5e05d23e5ee959014fb911d780e566545b@chromium.org>
Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#580953}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 803b80ff6b4e1f1512af111a59bbb97b0b7d9431
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