Extend hidl-gen to support generate vts file.

b/30762234

TODO: add regression test.

Change-Id: I1c31fd9a85805cd450ea03cc0ccc750a756d1009
diff --git a/ScalarType.cpp b/ScalarType.cpp
index bf111ca..b87168e 100644
--- a/ScalarType.cpp
+++ b/ScalarType.cpp
@@ -147,5 +147,15 @@
     handleError(out, mode);
 }
 
+
+status_t ScalarType::emitVtsTypeDeclarations(Formatter &out) const {
+    std::string extra;
+    out << "type: TYPE_SCALAR\n"
+        << "scalar_type: "
+        << getCppType(StorageMode_Stack, &extra)
+        << "\n";
+    return OK;
+}
+
 }  // namespace android