Classes under chromeos/dbus are supposed to provide nothing more than simple D-Bus bindings.
However, DebugDaemonClient provides a variety of features which are totally unrelated to D-Bus.

- Pipe IO: D-Bus is only responsible to pass FD from one process to another. Doing pipe IO over the FD is fine, but the code under chromeos/dbus it not the right place to do it.
- base::trace_event::TracingAgent implementation: Again, chromeos/dbus is not the right place to implement this.

We should make a new chromeos/ subdirectory (e.g. chromeos/debug, or chromeos/tracing), and move these features to a new class under that directory.