Fix microdump_writer and add unittest.

This adds some small fixes to the microdump writer and introduces
a unittest.

BUG=chromium:410294
R=mmandlis@chromium.org

Review URL: https://breakpad.appspot.com/2814002

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@1404 4c0a9323-5329-0410-9bdc-e9ce6186880e
4 files changed