On 'usual' Linux systems in '/proc/self/maps' we encounter two entries
per library: one has 'rw-p' attrs and the other has 'r-xp'. While on
Android, I see 'rwxp' and 'r-xp' (both entries are marked executable.)
So I've added an explicit check for non-writability to leave only a
single record in the log file.

Review URL: http://codereview.chromium.org/661467

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4018 ce2b1a6d-e550-0410-aec6-3dcde31c8c00