Add olivierrobin@chromium.org as owner

Running git log will reveal that Olivier has committed more than 40 CLs
this folders and given that he has been a committer for more than 6
months. He meets all the criteria.

Change-Id: I090289fa27abee24fcf9e46c916cb4287e15048a
Reviewed-on: https://chromium-review.googlesource.com/c/1348091Reviewed-by: Olivier Robin <olivierrobin@chromium.org>
Reviewed-by: Moe Ahmadi <mahmadi@chromium.org>
Commit-Queue: Javier Ernesto Flores Robles <javierrobles@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610629}

ios/chrome/browser/autofill/OWNERS

 mahmadi@chromium.org
+olivierrobin@chromium.org
 
 # TEAM: ios-directory-owners@chromium.org
 # OS: iOS

ios/chrome/browser/ui/autofill/OWNERS

 mahmadi@chromium.org
+olivierrobin@chromium.org
 
 # TEAM: ios-directory-owners@chromium.org
 # OS: iOS