[iOS] Store default search engine search-by-image status in UserDefaults

This value is needed in extensions, so we can use NSUserDefaults to
store it.

Bug: 913958
Change-Id: I4cacfb56c62e84e97a6529797bb97473715b5eb0
Reviewed-on: https://chromium-review.googlesource.com/c/1488911
Reviewed-by: Olivier Robin <olivierrobin@chromium.org>
Reviewed-by: Mark Cogan <marq@chromium.org>
Commit-Queue: Robbie Gibson <rkgibson@google.com>
Cr-Commit-Position: refs/heads/master@{#636918}
10 files changed