implement GetProcessExecutablePath() on OpenBSD and start using it

also add a way to override the hardcoded path in PathProviderPosix()
to ease development

BUG=
TEST=


Review URL: http://codereview.chromium.org/8390002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@107149 0039d316-1c4b-4281-b951-d872f2087c98
3 files changed