DevTools: Extract the "host" module from core_base

This change further reduces the number of "orphan" scripts and
brings the deployment model closer to the compilation one.

R=aandrey, vsevik

Review URL: https://codereview.chromium.org/367153006

git-svn-id: svn://svn.chromium.org/blink/trunk@177739 bbb929c8-8fbe-4397-9dbb-9b2b20218538