Fix MinidumpMiscInfoWriter test compilation with 32-bit time_t

Fix MinidumpMiscInfoWriter test compilation with 32-bit time_t.

This produced errors such as:
minidump_misc_info_writer_test.cc:665:32: error: non-constant-expression
cannot be narrowed from type 'uint32_t' (aka 'unsigned int') to
'__darwin_time_t' (aka 'long') in initializer list [-Wc++11-narrowing]
  const timeval kStartTime = { expect_misc_info.ProcessCreateTime, 0 };
                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
minidump_misc_info_writer_test.cc:665:32: note: override this message by
inserting an explicit cast
  const timeval kStartTime = { expect_misc_info.ProcessCreateTime, 0 };
                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                               static_cast<__darwin_time_t>(     )

TEST=minidump_test MinidumpMiscInfoWriter.InitializeFromSnapshot
R=rsesek@chromium.org

Committed: https://chromium.googlesource.com/crashpad/crashpad/+/408262d58fabff5a10211f23763fc40e9507c772

[Mark Mentovai, 2014-11-07 00:09:54]

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

[Robert Sesek, 2014-11-07 14:49:42]

LGTM

[Mark Mentovai, 2014-11-07 15:02:25]

Committed patchset #1 (id:1) manually as
408262d58fabff5a10211f23763fc40e9507c772 (presubmit successful).