[es6] emit error when for-in loop declarations are initialized in strict mode

src/messages.js

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // -------------------------------------------------------------------
 
 var kMessages = {
   // Error
   cyclic_proto:                  ["Cyclic __proto__ value"],
   code_gen_from_strings:         ["%0"],
@@ skipping 179 matching lines @@
   module_export_undefined:       ["Export '", "%0", "' is not defined in module"],
   duplicate_export:              ["Duplicate export of '", "%0", "'"],
   unexpected_super:              ["'super' keyword unexpected here"],
   extends_value_not_a_function:  ["Class extends value ", "%0", " is not a function or null"],
   prototype_parent_not_an_object: ["Class extends value does not have valid prototype property ", "%0"],
   duplicate_constructor:         ["A class may only have one constructor"],
   super_constructor_call:        ["A 'super' constructor call may only appear as the first statement of a function, and its arguments may not access 'this'. Other forms are not yet supported."],
   duplicate_proto:               ["Duplicate __proto__ fields are not allowed in object literals"],
   param_after_rest:              ["Rest parameter must be last formal parameter"],
   constructor_noncallable:       ["Class constructors cannot be invoked without 'new'"],
-  array_not_subclassable:        ["Subclassing Arrays is not currently supported."]
+  array_not_subclassable:        ["Subclassing Arrays is not currently supported."],
+  strict_for_in_loop_initializer: ["for-in loop variable declaration may not have an initializer in strict mode."],

[arv (Not doing code reviews), 2015/03/25 09:17:43]

This is misleading...

[caitp (gmail), 2015/03/25 11:22:42]

I know it's not technically allowed in sloppy mode, but I don't have telemetry
to know if it would break anyone. I'm more confident with strict-mode only (for
now) because of JSC is already doing that.

+  for_of_loop_initializer:       ["for-of loop variable declaration may not have an initializer."]
 };
 
 
 function FormatString(format, args) {
   var result = "";
   var arg_num = 0;
   for (var i = 0; i < format.length; i++) {
     var str = format[i];
     if (str.length == 2 && %_StringCharCodeAt(str, 0) == 0x25) {
       // Two-char string starts with "%".
@@ skipping 1117 matching lines @@
 function SetUpStackOverflowBoilerplate() {
   var boilerplate = MakeRangeError('stack_overflow', []);
 
   %DefineAccessorPropertyUnchecked(
       boilerplate, 'stack', StackTraceGetter, StackTraceSetter, DONT_ENUM);
 
   return boilerplate;
 }
 
 var kStackOverflowBoilerplate = SetUpStackOverflowBoilerplate();