fix(tests): fix avatar crop transition.

Fixes #1836 

The avatar_change tests should now pass here: http://tests.dev.lcip.org:8111/viewLog.html?buildId=172&buildTypeId=fxa_Tester&tab=buildLog
Another pass http://tests.dev.lcip.org:8111/viewLog.html?buildId=174&buildTypeId=fxa_Tester&tab=buildLog#_focus=275 seems like a good fix for now :)