Add PPDProvider barebones implementation and associated cache skeleton.

chromeos/printing/printer_configuration.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chromeos/printing/printer_configuration.h"
 
 #include <string>
 
 namespace chromeos {
 
 Printer::Printer() {}
 
 Printer::Printer(const std::string& id) : id_(id) {}
 
 Printer::Printer(const Printer& other) = default;
 
 Printer& Printer::operator=(const Printer& other) = default;
 
 Printer::~Printer() {}
 
-void Printer::SetPPD(std::unique_ptr<Printer::PPDFile> ppd) {
-  ppd_ = *(ppd.get());
-}
-
 }  // namespace chromeos