Extend hidl-gen to support generate vts file.

b/30762234

TODO: add regression test.

Change-Id: I1c31fd9a85805cd450ea03cc0ccc750a756d1009
diff --git a/EnumType.h b/EnumType.h
index 6453166..7aa55e5 100644
--- a/EnumType.h
+++ b/EnumType.h
@@ -37,6 +37,9 @@
     status_t emitTypeDeclarations(Formatter &out) const override;
     status_t emitJavaTypeDeclarations(Formatter &out) const override;
 
+    status_t emitVtsTypeDeclarations(Formatter &out) const override;
+    status_t emitVtsArgumentType(Formatter &out) const override;
+
 private:
     std::vector<EnumValue *> *mValues;
     Type *mStorageType;