DevTools: Rename inspector.js -> Main.js to follow the type name

R=aandrey, pfeldman, vsevik
NOTRY=true

Review URL: https://codereview.chromium.org/202763006

git-svn-id: svn://svn.chromium.org/blink/trunk@169542 bbb929c8-8fbe-4397-9dbb-9b2b20218538