Don't put internalized parser handles in a DeferredHandleScope if we aren't
going to compile concurrently since this has a performance cost.

BUG=chromium:686658

Change-Id: Id89d197b863569346895583e6df79134e79a5d4b
Reviewed-on: https://chromium-review.googlesource.com/461879Reviewed-by: Marja Hölttä <marja@chromium.org>
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44196}