This changes the way crash reports for child processes happening too early
during the child process' startup. Before bug 1547698 we wrote a partial
.extra file with those crashes that lacked the process type. The user would
not be notified of those crashes until she restarted Firefox and even when
submitted those crashes would be erroneously labeled as browser crashes.
After bug 1547698 we stopped writing .extra files entirely for those crashes
which left orphaned .dmp files among the pending crash reports.
This patch does three things to improve the situation:
* It writes a partial .extra file so that the crashes are detected at the next
startup. So the user is still not notified directly of these crashes but she
can report them later.
* It adds the process type to the .extra file so that the crash reporters are
labelled correctly.
* It fixes a leak in the `pidToMinidump` hash-map. Since the crashes were
not finalized the `ChildProcessData` strucutre associated with them would
never be fred.
Differential Revision: https://phabricator.services.mozilla.com/D40810
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extra : moz-landing-system : lando
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