Enforce naming conventions and allow empty (except for the header) types.hal files.
diff --git a/Type.h b/Type.h
index edf669b..e4d6d03 100644
--- a/Type.h
+++ b/Type.h
@@ -14,6 +14,7 @@
 
     virtual void dump(Formatter &out) const = 0;
     virtual bool isScope() const;
+    virtual bool isInterface() const;
 
 private:
     DISALLOW_COPY_AND_ASSIGN(Type);