Add PPDProvider barebones implementation and associated cache skeleton.

chromeos/printing/printer_configuration.h

Index: chromeos/printing/printer_configuration.h
diff --git a/chromeos/printing/printer_configuration.h b/chromeos/printing/printer_configuration.h
index fc82c293798c94a84e7f71e5216374fdf54c69d9..1d5bfcc727ea4d1bc5555aa711df9c190513e307 100644
--- a/chromeos/printing/printer_configuration.h
+++ b/chromeos/printing/printer_configuration.h
@@ -15,21 +15,32 @@ namespace chromeos {
 
 class CHROMEOS_EXPORT Printer {
  public:
-  // Represents a Postscript Printer Description with which the printer was
-  // setup.
-  struct PPDFile {
-    // Identifier from the quirks server. -1 otherwise.
-    int id = -1;
-
-    std::string file_name;
-
-    // If there is a file with a later version on the quirks server, that file
-    // should be used. The default value is 0.
-    int version_number = 0;
-
-    // This will be true if the file was retrived from the quirks server.
-    // Otherwise, the file was saved to disk by the user.
-    bool from_quirks_server = false;
+  // Information needed to find the PPD file for this printer.

[Lei Zhang, 2016/10/17 17:54:07]

Why is this still here? Didn't these changes land in
https://codereview.chromium.org/2408293002/ already? Please rebased.

[Carlson, 2016/10/18 19:05:01]

Done.

+  //
+  // If you add fields to this struct, you almost certainly will
+  // want to update PpdResolver and PpdCache::GetCachePath.
+  //
+  // 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.
+    std::string user_supplied_ppd_url;
+
+    // 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;
   };
 
   // Constructs a printer object that is completely empty.
@@ -68,8 +79,8 @@ class CHROMEOS_EXPORT Printer {
   const std::string& uri() const { return uri_; }
   void set_uri(const std::string& uri) { uri_ = uri; }
 
-  const PPDFile& ppd() const { return ppd_; }
-  void SetPPD(std::unique_ptr<PPDFile> ppd);
+  const PpdReference& ppd_reference() const { return ppd_reference_; }
+  PpdReference* mutable_ppd_reference() { return &ppd_reference_; }
 
   const std::string& uuid() const { return uuid_; }
   void set_uuid(const std::string& uuid) { uuid_ = uuid; }
@@ -94,8 +105,8 @@ class CHROMEOS_EXPORT Printer {
   // Contains protocol, hostname, port, and queue.
   std::string uri_;
 
-  // The associated postscript printer description.
-  PPDFile ppd_;
+  // How to find the associated postscript printer description.
+  PpdReference ppd_reference_;
 
   // The UUID from an autoconf protocol for deduplication. Could be empty.
   std::string uuid_;