Bug 837677 - [e-mail] Implement new startup loading events
Revert "Bug 1025565 - Only render the necessary icons when dragging. r=kgrandon"

This reverts commit 1c2db4082e7c7c5bdf18beea429d4b57b617fb87.
Merge pull request #20464 from jrburke/bug837677-email-startup-events

Bug 837677 - [e-mail] Implement new startup loading events r=mcav