Summary:
Currently Flipper.init is called as soon as the script loads.
However, if the store takes a bit longer than usual to get rehydrated, then this init call can get called before it has been set.
Fixing it by using a specific event instead of the generic `onload`.
Reviewed By: passy
Differential Revision: D17711399
fbshipit-source-id: fcaf9e5943bfd15359038b8e3722f11d7e06379b