The crumbs Crashpad extensions need to know the location of the user data dir on Chrome and Chrome.exe has some other quirky command line requirements. As-is this is dealt with in crash_reporter::internal::PlatformCrashpadInitialization, which is common to at least setup.exe and chrome.exe, which is confusing.
A better way to do this is to extend the crash_reporter::CrashReporterClient interface and allow this command line manipulation to be performed per embedder/client.