Lazily create PPDCache directory on first store.

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>
 
@@ skipping 28 matching lines @@
     base::TimeDelta max_available_list_staleness =
         base::TimeDelta::FromDays(14);
 
     // Size limit on the serialized cached available printer list, in bytes.
     // This is just a check to make sure we don't consume ridiculous amounts of
     // disk if we get bad data.
     // Default is 10 MB
     size_t max_available_list_cached_size = 10 * 1024 * 1024;
   };
 
-  // Create and return a Ppdcache that uses cache_dir to store state.
+  // Create and return a Ppdcache that uses cache_dir to store state.  If
+  // cache_base_dir does not exist, it will be lazily created the first time the
+  // cache needs 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 be non-empty and
   // remain valid until the next Store() call.
@@ skipping 23 matching lines @@
   // Store |available_printers|, replacing any existing entry.
   virtual void StoreAvailablePrinters(
       std::unique_ptr<PpdProvider::AvailablePrintersMap>
           available_printers) = 0;
 };
 
 }  // namespace printing
 }  // namespace chromeos
 
 #endif  // CHROMEOS_PRINTING_PPD_CACHE_H_