Extend hidl-gen to support generate vts file.

b/30762234

TODO: add regression test.

Change-Id: I1c31fd9a85805cd450ea03cc0ccc750a756d1009
diff --git a/Type.cpp b/Type.cpp
index 1e7e2d5..59439c3 100644
--- a/Type.cpp
+++ b/Type.cpp
@@ -255,5 +255,13 @@
     out << ");\n";
 }
 
+status_t Type::emitVtsTypeDeclarations(Formatter &) const {
+    return OK;
+}
+
+status_t Type::emitVtsArgumentType(Formatter &out) const {
+    return emitVtsTypeDeclarations(out);
+}
+
 }  // namespace android