Clean up code generator before implementing [ExposeV8GetterAndSetter]

This CL just renames variables to make the main change diff saner.

NOTRY=true

Review URL: https://codereview.chromium.org/54123003

git-svn-id: svn://svn.chromium.org/blink/trunk@161030 bbb929c8-8fbe-4397-9dbb-9b2b20218538