sync: add WIFI_CREDENTIALS protobuf, ModelType, and preference

sync/protocol/proto_value_conversions.h

Index: sync/protocol/proto_value_conversions.h
diff --git a/sync/protocol/proto_value_conversions.h b/sync/protocol/proto_value_conversions.h
index 2a3c1ae1b8a4865dba99ed3fbd4488ed5e99abbb..79e4ca2197d35bb51a369cab4115bb5624355aec 100644
--- a/sync/protocol/proto_value_conversions.h
+++ b/sync/protocol/proto_value_conversions.h
@@ -78,6 +78,7 @@ class Target;
 class ThemeSpecifics;
 class TimeRangeDirective;
 class TypedUrlSpecifics;
+class WifiCredentialSpecifics;
 }  // namespace sync_pb
 
 // Utility functions to convert sync protocol buffers to dictionaries.
@@ -274,6 +275,9 @@ SYNC_EXPORT_PRIVATE base::DictionaryValue* ThemeSpecificsToValue(
 SYNC_EXPORT_PRIVATE base::DictionaryValue* TypedUrlSpecificsToValue(
     const sync_pb::TypedUrlSpecifics& typed_url_specifics);
 
+SYNC_EXPORT_PRIVATE base::DictionaryValue* WifiCredentialSpecificsToValue(
+    const sync_pb::WifiCredentialSpecifics& wifi_credential_specifics);
+
 // Any present extensions are mapped to sub-dictionary values with the
 // key equal to the extension name.
 SYNC_EXPORT_PRIVATE base::DictionaryValue* EntitySpecificsToValue(