For-of statements do not permit initializers.

test/mjsunit/harmony/iteration-syntax.js

Index: test/mjsunit/harmony/iteration-syntax.js
diff --git a/test/mjsunit/harmony/iteration-syntax.js b/test/mjsunit/harmony/iteration-syntax.js
index 21149c04bc99108beb802fcfd65a253a558aae42..3bda78ed4e16d312d7f3351a9c60158659f99e1a 100644
--- a/test/mjsunit/harmony/iteration-syntax.js
+++ b/test/mjsunit/harmony/iteration-syntax.js
@@ -54,6 +54,11 @@ assertThrows("function f() { for (var of of) { } }", SyntaxError);
 assertThrows("function f() { for (let of y) { } }", SyntaxError);
 assertThrows("function f() { for (let of of) { } }", SyntaxError);
 
+assertThrows("function f() { for (x = 3 of y) { } }", SyntaxError);
+assertThrows("function f() { for (var x = 3 of y) { } }", SyntaxError);
+assertThrows("function f() { for (let x = 3 of y) { } }", SyntaxError);
+
+
 // Alack, this appears to be valid.
 function f() { for (of of y) { } }
 function f() { for (let of of y) { } }