Disconnecting the GMPCrashHelpers at the right time is hard, because in the
crashing case we're all shutdown before the GMPCrashHelpers can be invoked to
help handle the crash report. So add a class to help the helpers;
GMPCrashHelperHolder. This composes into the GMP content protocol actors, to
help them disconnect the crash helpers at the right time. See the comment in
GMPCrashHelperHolder for the details.
MozReview-Commit-ID: E5rE6e5Jues
--HG--
extra : rebase_source : f688bf727f23f773eb995611cec6412ebf021029
