Refactoring: Make script dependencies more object-oriented in push and merge scripts.

- Connect the top-level scripts via inheritance and remove top-level functions
- Options and option processing can be extended from base to subclass script

This CL is split off from https://codereview.chromium.org/173983002/

BUG=
R=ulan@chromium.org

Review URL: https://codereview.chromium.org/185263003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19664 ce2b1a6d-e550-0410-aec6-3dcde31c8c00