Add fd input (such as socket) event to shill_event

It's understood that the main event loop is changing, but
here's a first cut at describing the sort of things we will
need in that respect.  I'm using this facility for my RTNL
prototype.

BUG=n0ne (this will likely be overwritten)
TEST=Unit tests added to unittest.cc and pass

Change-Id: I4ee89fc4119da0871e9f852707cce9341a5018c0
Reviewed-on: http://gerrit.chromium.org/gerrit/605
Reviewed-by: Chris Masone <cmasone@chromium.org>
Tested-by: Paul Stewart <pstew@chromium.org>
3 files changed