Towards removing use of open() with O_EXLOCK/O_SHLOCK in code
used on non-BSD.
Adds simple Thread abstraction to util/test.
Includes mini_chromium roll with:
56dd2883170d0df0ec89af0e7862af3f9aaa9be6 Fix import of atomicops for Windows
886592fd6677615c54c4156bb2f2edb5d547ba6c Export SystemErrorCodeToString
R=mark@chromium.org, rsesek@chromium.org
BUG=crashpad:1, crashpad:13
Review URL: https://codereview.chromium.org/1001673002