Simplify fix for jashkenas#4464

This uses more of the existing machinery for moving class body
expressions into the initializer.

Author: connec

lib/coffeescript/nodes.js

@@ -1760,11 +1760,10 @@ exports.Class = class Class extends Base
 
 
   # Add an expression to the class initializer
-  #
-  # NOTE Currently, only methods and static methods are valid in ES class initializers.
-  # When additional expressions become valid, this method should be updated to handle them.
   addInitializerExpression: (node) ->
-    if @validInitializerMethod node
+    if node.unwrapAll() instanceof PassthroughLiteral
+      node
+    else if @validInitializerMethod node
       @addInitializerMethod node
     else
       null