win: Make StartHandler() restrict HANDLES inherited by crashpad_handler
win: Make StartHandler() restrict HANDLES inherited by crashpad_handler

This requires Windows NT 6.0 (Vista and Server 2008). On earlier
operating system versions, the existing behavior of inheriting all
inheritable handles is retained.

BUG=crashpad:69
R=scottmg@chromium.org

Review URL: https://codereview.chromium.org/1427273003 .

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