Summary:
Why does message-list have default participants? No other packages do
Component registry warns if mixin component name not found
Clear the component registry between tests and wipe React elements inserted into DOM
Everything should have a displayName, even you ComposerView
Stub all ComponentRegistry dependencies, always
Test Plan: Run all the tests at the same time
Reviewers: evan
Reviewed By: evan
Differential Revision: https://review.inboxapp.com/D1201