[es6] Class extends may not be a generator function

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
   constructor_is_generator:      ["Class constructor may not be a generator"],
   constructor_is_accessor:       ["Class constructor may not be an accessor"],
@@ skipping 137 matching lines @@
   strong_constructor_return_misplaced: ["In strong mode, returning from a constructor before its super constructor invocation is deprecated"],
   sloppy_lexical:                ["Block-scoped declarations (let, const, function, class) not yet supported outside strict mode"],
   malformed_arrow_function_parameter_list: ["Malformed arrow function parameter list"],
   cant_prevent_ext_external_array_elements: ["Cannot prevent extension of an object with external array elements"],
   redef_external_array_element:  ["Cannot redefine a property of an object with external array elements"],
   const_assign:                  ["Assignment to constant variable."],
   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"],
+  extends_value_generator:       ["Class extends value ", "%0", " may not be a generator function"],
   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."],
   for_in_loop_initializer:       ["for-in loop variable declaration may not have an initializer."],
   for_of_loop_initializer:       ["for-of loop variable declaration may not have an initializer."],
   for_inof_loop_multi_bindings:  ["Invalid left-hand side in ", "%0", " loop: Must have a single binding."],
@@ skipping 1094 matching lines @@
 function SetUpStackOverflowBoilerplate() {
   var boilerplate = MakeRangeError(kStackOverflow);
 
   %DefineAccessorPropertyUnchecked(
       boilerplate, 'stack', StackTraceGetter, StackTraceSetter, DONT_ENUM);
 
   return boilerplate;
 }
 
 var kStackOverflowBoilerplate = SetUpStackOverflowBoilerplate();