packager: optimize assets' JS

Reviewed By: davidaurelio

Differential Revision: D5010186

fbshipit-source-id: 3c26d8b8792df1dbc24e5200f28f63e017cb0173

packager/src/ModuleGraph/types.flow.js

@@ -152,6 +152,7 @@ export type TransformedSourceFile =
 
 export type LibraryOptions = {|
   dependencies?: Array<string>,
+  optimize: boolean,
   platform?: string,
   rebasePath: string => string,
 |};