Getting closer... Some tests passed on the last run, but the ones that
rely on having ntdll symbols fail on the bot. With `_NT_SYMBOL_PATH`
set, cdb will be able to download the PDBs so will be able to dump
data for `ntdll!_PEB`, etc.
R=mark@chromium.org
BUG=crashpad:46
Review URL: https://codereview.chromium.org/1402643002 .