DevTools: Introduce binding entities for the CSS and debugger domains

Introduced are CSSPresentationModel and DebuggerPresentationModel,
intended to ultimately remove all sdk-workspace bindings from
purely sdk entities. This patch solely migrates the clients
to the new API, leaving the behavior largely intact.

R=vsevik@chromium.org, vsevik

Review URL: https://codereview.chromium.org/397263002

git-svn-id: svn://svn.chromium.org/blink/trunk@178636 bbb929c8-8fbe-4397-9dbb-9b2b20218538