DevTools: Build function details' raw location in DebuggerModel

Previously, it was the clients' responsibility to build raw locations
based on DebuggerAgent.Location.

R=vsevik

Review URL: https://codereview.chromium.org/402873002

git-svn-id: svn://svn.chromium.org/blink/trunk@178457 bbb929c8-8fbe-4397-9dbb-9b2b20218538