Add PPDProvider barebones implementation and associated cache skeleton.

chromeos/chromeos.gyp

Index: chromeos/chromeos.gyp
diff --git a/chromeos/chromeos.gyp b/chromeos/chromeos.gyp
index 13142d29564011b390371b8fb01b196c22acd8fb..7b12e01584afff9139f5c0fe05fa00e589d7e99c 100644
--- a/chromeos/chromeos.gyp
+++ b/chromeos/chromeos.gyp
@@ -343,6 +343,10 @@
       'network/shill_property_handler.h',
       'network/shill_property_util.cc',
       'network/shill_property_util.h',
+      'printing/ppd_cache.cc',
+      'printing/ppd_cache.h',
+      'printing/ppd_provider.cc',
+      'printing/ppd_provider.h',
       'printing/printer_configuration.cc',
       'printing/printer_configuration.h',
       'printing/printer_translator.h',
@@ -455,6 +459,7 @@
       'network/onc/onc_validator_unittest.cc',
       'network/prohibited_technologies_handler_unittest.cc',
       'network/shill_property_handler_unittest.cc',
+      'printing/ppd_provider_unittest.cc',
       'printing/printer_translator_unittest.cc',
       'process_proxy/process_output_watcher_unittest.cc',
       'process_proxy/process_proxy_unittest.cc',