[ObjC ARC] Converts ios/chrome/browser/ui/popup_menu:popup_menu to ARC.

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

Review-Url: https://codereview.chromium.org/2935743002
Cr-Commit-Position: refs/heads/master@{#478977}
5 files changed