Add PPDProvider barebones implementation and associated cache skeleton.

chromeos/printing/ppd_cache.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_PPD_CACHE_H_
+#define CHROMEOS_PRINTING_PPD_CACHE_H_
+
+#include <memory>
+#include <string>
+
+#include "base/files/file_path.h"
+#include "base/optional.h"
+#include "chromeos/chromeos_export.h"
+#include "chromeos/printing/printer_configuration.h"
+
+namespace chromeos {
+namespace printing {
+
+// PpdCache manages a cache of locally-stored ppd files.  At its core,
+// it operates like a persistent hash from PpdReference to files.  If

[skau, 2016/10/14 22:10:16]

hash?  do you mean mapping?

+// you give the same PpdReference to Find that was previously passed

[skau, 2016/10/14 22:10:16]

typo?

+// to
+class CHROMEOS_EXPORT PpdCache {
+ public:
+  // Construction-time optional parameters.  These should all have defaults that
+  // are sane.
+  struct Options {
+    // Nothing here yet.  We may want to add ttl-style options here eventually
+    // so the cache doesn't grow without bound.
+  };
+
+  // Create and return a Ppdcache that uses cache_dir to store state.
+  static std::unique_ptr<PpdCache> Create(const base::FilePath& cache_base_dir,
+                                          const Options& options = Options());
+  virtual ~PpdCache() {}
+
+  // Find a PPD that was previously cached with the given reference.  Note that
+  // all fields of the reference must be the same, otherwise we'll miss in the
+  // cache and re-run resolution for the PPD.
+  //
+  // If a FilePath is returned, it is guaranteed to remain valid until the next
+  // Store() call.
+  virtual base::Optional<base::FilePath> Find(
+      const Printer::PpdReference& reference) const = 0;
+
+  // Take the contents of a ppd file, store it to the cache, and return the
+  // path to the stored file keyed on reference.
+  //
+  // If a different ppd was previously Stored for the given reference, it
+  // will be replaced.
+  //
+  // On success, the returned FilePath is guaranteed to remain valid until the
+  // next Store* call.
+  virtual base::Optional<base::FilePath> Store(
+      const Printer::PpdReference& reference,
+      const std::string& ppd_contents) = 0;
+};
+
+}  // namespace printing
+}  // namespace chromeos
+
+#endif  // CHROMEOS_PRINTING_PPD_CACHE_H_