The new ObjectPtr design makes non-inlined helper functions a little
more expensive because "this" is always a pointer where pass-by-value
would be more efficient, which is an issue for functions whose size puts
them right at the threshold of getting inlined or not. String::Get falls
into this category when called from RegExpFlagsFromString. In this case,
we can do even better than restoring inlineability by fine-tuning
the control flow a bit.

This should repair the regression in crbug.com/910573

Bug: chromium:910573
Change-Id: Ie6b68ef01cd978ec502d8d6c1da788c77422dce7
Reviewed-on: https://chromium-review.googlesource.com/c/1369087
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58234}