Completely rewrite the PpdProvider/PpdCache to use the SCS backend. Along the way, clean it up a l…

components/sync/protocol/printer_specifics.proto

 // 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.
 //
 // Sync protocol datatype extension for printer data.
 
 // Update proto_value_conversions{.h,.cc,_unittest.cc} if you change
 // any fields in this file.
 
 syntax = "proto2";
 
 option optimize_for = LITE_RUNTIME;
 
 package sync_pb;
 
 // User PPD configuration
 message PrinterPPDReference {
   // Url for user provided file.  Overrides other fields.
   optional string user_supplied_ppd_url = 1;
 
-  // Make and model to reference into PPD Server.
-  optional string effective_manufacturer = 2;
-  optional string effective_model = 3;
+  // Retired fields
+  optional string effective_manufacturer = 2 [deprecated = true];
+  optional string effective_model = 3 [deprecated = true];
+
+  // String identifying the type of printer, used to look up a ppd to drive the
+  // printer.
+  optional string effective_make_and_model = 4;
 }
 
 message PrinterSpecifics {
   // Printer record GUID
   optional string id = 1;
 
   // User visible name.  Any string.
   optional string display_name = 2;
 
   // User visible description.  Any string.
@@ skipping 16 matching lines @@
 
   // PPDData was deprecated in favor of PPDReference format.
   optional bytes ppd = 8 [deprecated = true];
 
   // Structure representing the user's ppd configuration.
   optional PrinterPPDReference ppd_reference = 9;
 
   // Timestamp when printer was last updated.
   optional int64 updated_timestamp = 10;
 }