[Autofill] Fix the AutofillManager constructor

Was using hardcoded locale.

Bug: None
Test: existing
Change-Id: I9a86d2acccd0821c7e734661df2c95953f043951
Reviewed-on: https://chromium-review.googlesource.com/781404


Reviewed-by: Sebastien Seguin-Gagnon <sebsg@chromium.org>
Commit-Queue: Mathieu Perreault <mathp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#518297}