offsets in the MemoryMap are expressed as two's complement while
Crashpad's and mini_chromium's string conversion functions expect
negative numbers to be expressed with a '-' character.
Convert the string as unsigned and then re-interpret to signed when
necessary.
Bug: 914246
Change-Id: I76aaf092ea7ad98806be7a3f380dab4ca0425ed6
Reviewed-on: https://chromium-review.googlesource.com/c/1399372
Reviewed-by: Joshua Peraza <jperaza@chromium.org>
Commit-Queue: Joshua Peraza <jperaza@chromium.org>