Create a fresh sync datatype for Synced Notifications

sync/protocol/sync.proto

Index: sync/protocol/sync.proto
diff --git a/sync/protocol/sync.proto b/sync/protocol/sync.proto
index 6877ece4927003f2c04c13bd27a353552fa4f318..560245b866017d4e52240b207d200d660d7b210d 100644
--- a/sync/protocol/sync.proto
+++ b/sync/protocol/sync.proto
@@ -31,6 +31,7 @@ import "history_delete_directive_specifics.proto";
 import "nigori_specifics.proto";
 import "password_specifics.proto";
 import "preference_specifics.proto";
+import "push_notifications_specifics.proto";
 import "search_engine_specifics.proto";
 import "session_specifics.proto";
 import "sync_enums.proto";
@@ -101,6 +102,7 @@ message EntitySpecifics {
   optional ExtensionSettingSpecifics extension_setting = 96159;
   optional AppSettingSpecifics app_setting = 103656;
   optional HistoryDeleteDirectiveSpecifics history_delete_directive = 150251;
+  optional PushNotificationsSpecifics push_notifications = 153108;
   optional DeviceInfoSpecifics device_info = 154522;
   optional ExperimentsSpecifics experiments = 161496;
 }