Deduplicate a CreateExtensionPrefStore helper function

Noticed while experimenting with jumbo in chrome/browser. Symbols
that are duplicated cause compilation problems if they end up
in the same translation unit.

Bug: 746957
Change-Id: I07a5bcb690026359e7d74be81a0a26ce9f40958b
Reviewed-on: https://chromium-review.googlesource.com/846747
Commit-Queue: Daniel Bratell <bratell@opera.com>
Reviewed-by: Bernhard Bauer <bauerb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#527631}
4 files changed