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

chromeos/printing/printer_configuration.h

 // 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.
 
 #ifndef CHROMEOS_PRINTING_PRINTER_CONFIGURATION_H_
 #define CHROMEOS_PRINTING_PRINTER_CONFIGURATION_H_
 
 #include <memory>
 #include <string>
 
 #include "base/macros.h"
 #include "chromeos/chromeos_export.h"
 
 namespace chromeos {
 
 class CHROMEOS_EXPORT Printer {
  public:
   // Information needed to find the PPD file for this printer.
   //
   // If you add fields to this struct, you almost certainly will
   // want to update PpdResolver and PpdCache::GetCachePath.
   //
+  // Exactly one of the fields below should be filled in.
+  //
   // At resolution time, we look for a cached PPD that used the same
   // PpdReference before.
   //
-  // If one is not found and user_supplied_ppd_url is set, we'll fail
-  // out with NOT FOUND
-  //
-  // Otherwise, we'll hit QuirksServer to see if we can resolve a Ppd
-  // using manufacturer/model
   struct PpdReference {
     // If non-empty, this is the url of a specific PPD the user has specified
-    // for use with this printer.
+    // for use with this printer.  The ppd can be gzipped or uncompressed.
     std::string user_supplied_ppd_url;

[skau, 2017/01/27 01:37:01]

Note: Technically, this is a uri rather than a url since it's usual the path to
a file. e.g. file:///home/user/...../PrinterPrinter.ppd.gz

[Carlson, 2017/01/27 18:48:43]

I've always been a little hazy on the distinction, so I went and did some
digging.

https://www.ietf.org/rfc/rfc1738.txt section 3.10 seems pretty definitive that
file:// does indeed fall into the scope of URL's, not just URIs.

 
-    // The *effective* manufacturer and model of this printer, in other words,
-    // the manufacturer and model of the printer for which we grab a PPD.  This
-    // doesn’t have to (but can) be the actual manufacturer/model of the
-    // printer.  We should always try to fill these fields in, even if we don’t
-    // think they’ll be needed, as they provide a fallback mechanism for
-    // finding a PPD.
-    std::string effective_manufacturer;
-    std::string effective_model;
+    // String that identifies which ppd to use from the ppd server.
+    // Where possible, this is the same as the ipp/ldap
+    // printer-make-and-model field.
+    std::string effective_make_and_model;
   };
 
   // The location where the printer is stored.
   enum Source {
     SRC_USER_PREFS,
     SRC_POLICY,
   };
 
   // Constructs a printer object that is completely empty.
   Printer();
@@ skipping 71 matching lines @@
   // The UUID from an autoconf protocol for deduplication. Could be empty.
   std::string uuid_;
 
   // The datastore which holds this printer.
   Source source_;
 };
 
 }  // namespace chromeos
 
 #endif  // CHROMEOS_PRINTING_PRINTER_CONFIGURATION_H_