Summary: `weakToStrong` where the keys are NSNumbers that aren't strongly held by anyone means the events in the table get removed almost immediately. Derp.
Test Plan: Confirm that events are not dropped from the table after they're added. Confirm that the "Search" button actually works in the Share Sheet.
Reviewers: suv, zsh, nyn531, kimon, bcunning, sma, grp, nadi, b3ll
Reviewed By: b3ll
Differential Revision: https://phabricator.fb.com/D1819759
Tasks: 6137402
Signature: t1:1819759:1422918745:bf25bc2662f767fec3a78fc0c7702c591ed17064
Fix regression from the ARC conversion. Change the raw, unretained
pointers in ASControlNode to weak references. Use NSMapTable instead of
the pointer-as-NSValue system.
