minidump: Be consistent about setting the fields of WritableIoVec

minidump: Be consistent about setting the fields of WritableIoVec.

The iov_base field appears before the iov_len field, but for some
reason, sometimes the fields were being set in the reverse order.

TEST=minidump_test
R=rsesek@chromium.org

Committed: https://chromium.googlesource.com/crashpad/crashpad/+/dcdbd2098f64b61a708ab2e1c0d0bd2acdc469f2

[Mark Mentovai, 2014-10-23 20:48:26]

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

[Mark Mentovai, 2014-10-23 20:48:27]

I hit this earlier today, and wound up reversing the fields. There’s no good
reason to do this backwards, especially in such close proximity to code that
does it in a different order.

[Robert Sesek, 2014-10-23 20:53:11]

LGTM

[Mark Mentovai, 2014-10-23 21:25:26]

Committed patchset #1 (id:1) manually as
dcdbd2098f64b61a708ab2e1c0d0bd2acdc469f2 (presubmit successful).