This is a follow-up to bug 1409249. There are a lot of places where our
factory singleton constructors either don't correctly handle their returned
references being released by the component manager, or do handle it, but in
ways that are not obvious.
This patch handles a few places where we can sometimes wind up with dangling
singleton pointers, adds some explanatory comments and sanity check
assertions, and replaces some uses of manual refcounting with StaticRefPtr and
ClearOnShutdown.
There are still some places where we may wind up with odd behavior if the
first QI for a getService call fails. In those cases, we wind up destroying
the first instance of a service that we create, and re-creating a new one
later.
MozReview-Commit-ID: ANYndvd7aZx
