Add check for executable stack/heap when rating Linux exploitability.

This CL also consequentially adds a public method to get the number of
mappings in a Linux minidump.

R=ivanpe@chromium.org

Review URL: https://codereview.chromium.org/1291603002

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@1488 4c0a9323-5329-0410-9bdc-e9ce6186880e
6 files changed