IWYU in minidump_writer.cc to fix building with libc++ after r1385.

R=ivanpe@chromium.org

Review URL: https://breakpad.appspot.com/6744002

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@1386 4c0a9323-5329-0410-9bdc-e9ce6186880e
Fix some nits raised by Timur for r1385.

R=ivanpe@chromium.org

Review URL: https://breakpad.appspot.com/1734002

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@1387 4c0a9323-5329-0410-9bdc-e9ce6186880e