[strong] Implement static restrictions on binding 'undefined' in arrow functions

test/mjsunit/strong/undefined.js

Index: test/mjsunit/strong/undefined.js
diff --git a/test/mjsunit/strong/undefined.js b/test/mjsunit/strong/undefined.js
index 8fc213d198ff79b7f9e43a93c2cd2287dd2d2014..870891f09a5b522b0de7dd96725c48133c79c1f5 100644
--- a/test/mjsunit/strong/undefined.js
+++ b/test/mjsunit/strong/undefined.js
@@ -107,11 +107,6 @@ assertThrows("({ foo(a, b, undefined, c, d) {'use strong';} });", SyntaxError);
 CheckStrongMode("({ *foo(a, b, undefined, c, d) {} });");
 assertThrows("({ *foo(a, b, undefined, c, d) {'use strong';} });", SyntaxError);
 
-// Arrow function expression with 'undefined' param
-// TODO(conradw): Checking arrow function heads is hard to modify just now
-// CheckStrongMode("(undefined => {})");
-// assertThrows("(undefined => {'use strong';})");
-
 // Class declaration named 'undefined'
 CheckStrongMode("class undefined {}");
 assertThrows("class undefined {'use strong'}", SyntaxError);