Make ios browser state directory creation always synchronous.

This is the ios mirror to
https://chromium-review.googlesource.com/c/613683

NOPRESUBMIT=True (for intentional ScopedAllowIO usage)

Bug: 755157, 689520
Change-Id: I856a31ce1e2fc930587e04e5b32c49b19161e155
Reviewed-on: https://chromium-review.googlesource.com/618087
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#495138}
1 file changed