This deduplicates/merges app memory regions so that we don't generate overlapping
memory regions in the minidump. We need to do this because older version of
dbghelp.dll (e.g. that on Windows 7) doesn't handle overlaps in its memory list,
which causes xpcshell bustages.
The test bustages are fixed by sorting and merging app memory regions before
adding to the input to the MinidumpWriteDump callback. Memory regions on the thread
stack is also excluded because thread stack memory is included in the minidump
by default.
MozReview-Commit-ID: 541vzG0b0kC
2a041b5a52