Convert NULL to nullptr

Convert NULL to nullptr.

This change was generated mechanically by running:

  find . \( -name \*.cc -or -name \*.mm -or -name \*.h \) \
      -and -not -path ./third_party/\* -and -not -path ./out/\* \
      -exec sed -i '' -E -e 's/(^|[^_])NULL/\1nullptr/g' {} +

Further manual fix-ups were applied to remove casts of nullptr to other
pointer types where possible, to preserve the intentional use of NULL
(as a short form of MACH_PORT_NULL) in exception_port_tool, and to fix
80-column violations.

https://groups.google.com/a/chromium.org/d/topic/chromium-dev/4mijeJHzxLg/discussion

TEST=*_test
R=rsesek@chromium.org

Committed: https://chromium.googlesource.com/crashpad/crashpad/+/5d74f120fc5797135d42f6bebf9ab80c49cc4a70

[Mark Mentovai, 2014-10-14 03:56:08]

mark@chromium.org changed reviewers:
+ rsesek@chromium.org

[Robert Sesek, 2014-10-14 13:51:26]

LGTM.

This thread discusses using just "null" in comments instead of "nullptr". I kind
of agree, but I don't think it matters all that much:
https://groups.google.com/a/chromium.org/d/msg/chromium-dev/oQunP1HmIfs/_7iCj...

[Mark Mentovai, 2014-10-14 14:04:54]

It’s pedantic, but given the documentation style in Crashpad, I could see
justifications for using either `nullptr` or null, but not `null`. The backticks
are already all there, so `nullptr` should be fine.

[Mark Mentovai, 2014-10-14 15:10:53]

Committed patchset #4 (id:60001) manually as
5d74f120fc5797135d42f6bebf9ab80c49cc4a70 (presubmit successful).