[Sync] Add history delete directive type

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 a1e938bb2a4ae3d7a8d05d6f527504d88a58ce41..81894c53a217e447f3a2679a067126c420607d8e 100644
--- a/sync/protocol/proto_value_conversions.h
+++ b/sync/protocol/proto_value_conversions.h
@@ -26,6 +26,7 @@ class EncryptedData;
 class EntitySpecifics;
 class ExtensionSettingSpecifics;
 class ExtensionSpecifics;
+class HistoryDeleteDirectiveSpecifics;
 class NigoriSpecifics;
 class PasswordSpecifics;
 class PasswordSpecificsData;
@@ -112,6 +113,10 @@ base::DictionaryValue* ExtensionSettingSpecificsToValue(
 base::DictionaryValue* ExtensionSpecificsToValue(
     const sync_pb::ExtensionSpecifics& extension_specifics);
 
+base::DictionaryValue* HistoryDeleteDirectiveSpecificsToValue(
+    const sync_pb::HistoryDeleteDirectiveSpecifics&
+        history_delete_directive_specifics);
+
 base::DictionaryValue* NigoriSpecificsToValue(
     const sync_pb::NigoriSpecifics& nigori_specifics);