arc: Create sync protos for Arc package.

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 91eff378fb22f5e14553b1e6dae95b652e245a61..311ed14afca5bf13589308eb979afd08606b7628 100644
--- a/sync/protocol/proto_value_conversions.h
+++ b/sync/protocol/proto_value_conversions.h
@@ -21,6 +21,7 @@ class AppNotification;
 class AppNotificationSettings;
 class AppSettingSpecifics;
 class AppSpecifics;
+class ArcPackageSpecifics;
 class ArticleSpecifics;
 class AttachmentIdProto;
 class AutofillProfileSpecifics;
@@ -110,6 +111,10 @@ SYNC_EXPORT std::unique_ptr<base::DictionaryValue> AppSettingsToValue(
 SYNC_EXPORT std::unique_ptr<base::DictionaryValue> LinkedAppIconInfoToValue(
     const sync_pb::LinkedAppIconInfo& linked_app_icon_info);
 
+// Sub-protocol of ArcPackageSpecifics.
+SYNC_EXPORT std::unique_ptr<base::DictionaryValue> ArcPackageSpecificsToValue(
+    const sync_pb::ArcPackageSpecifics& proto);
+
 // Sub-protocols of SessionSpecifics.
 
 SYNC_EXPORT std::unique_ptr<base::DictionaryValue> SessionHeaderToValue(