Currently, it executes the OWNERS check and tools/presubmit.py, as well as a
check for a non-empty commit message

BUG=none
TEST=run git cl presubmit

Review URL: https://codereview.chromium.org/11092002
Patch from Jochen Eisinger <jochen@chromium.org>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12678 ce2b1a6d-e550-0410-aec6-3dcde31c8c00