Extend hidl-gen to support generate vts file.

b/30762234

TODO: add regression test.

Change-Id: I1c31fd9a85805cd450ea03cc0ccc750a756d1009
diff --git a/ArrayType.h b/ArrayType.h
index 0a245f8..1d8ec1f 100644
--- a/ArrayType.h
+++ b/ArrayType.h
@@ -42,6 +42,8 @@
             const std::string &argName,
             bool isReader) const override;
 
+    status_t emitVtsTypeDeclarations(Formatter &out) const override;
+
 private:
     Type *mElementType;
     std::string mDimension;