[fidlc] Selector attribute only on methods

FIDL-381 #done

Test: cq
Change-Id: I01413da08a240caae2c09fcf2f04385b1a056a70
diff --git a/system/host/fidl/lib/flat_ast.cpp b/system/host/fidl/lib/flat_ast.cpp
index e4a3442..39613e0 100644
--- a/system/host/fidl/lib/flat_ast.cpp
+++ b/system/host/fidl/lib/flat_ast.cpp
@@ -511,6 +511,11 @@
         "Simple",
     },
     SimpleLayoutConstraint));
+    AddAttributeSchema("Selector", AttributeSchema({
+        AttributeSchema::Placement::kMethod,
+    }, {
+        /* any value */
+    }));
     AddAttributeSchema("Transport", AttributeSchema({
         AttributeSchema::Placement::kInterfaceDecl,
     }, {