[ObjC ARC] Converts ios/public/provider/chrome/browser/external_search:test_support to ARC.

Automatically generated ARCMigrate commit
Notable issues:None
BUG=624363
TEST=None

Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I178dd59af7a4d83a4eeee8543f63ee308832ca46
Reviewed-on: https://chromium-review.googlesource.com/844715
Reviewed-by: Mark Cogan <marq@chromium.org>
Commit-Queue: Stepan Khapugin <stkhapugin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#526289}
2 files changed