Fix error message for Object.observe accept argument

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 63 matching lines @@
   handler_returned_undefined:    ["Proxy handler ", "%0", " returned undefined from '", "%1", "' trap"],
   proxy_prop_not_configurable:   ["Proxy handler ", "%0", " returned non-configurable descriptor for property '", "%2", "' from '", "%1", "' trap"],
   proxy_non_object_prop_names:   ["Trap '", "%1", "' returned non-object ", "%0"],
   proxy_repeated_prop_name:      ["Trap '", "%1", "' returned repeated property name '", "%2", "'"],
   invalid_weakmap_key:           ["Invalid value used as weak map key"],
   invalid_weakset_value:         ["Invalid value used in weak set"],
   not_date_object:               ["this is not a Date object."],
   observe_non_object:            ["Object.", "%0", " cannot ", "%0", " non-object"],
   observe_non_function:          ["Object.", "%0", " cannot deliver to non-function"],
   observe_callback_frozen:       ["Object.observe cannot deliver to a frozen function object"],
-  observe_invalid_accept:        ["Object.observe accept must be an array of strings."],
+  observe_invalid_accept:        ["Third argument to Object.observe must be an array of strings."],
   observe_type_non_string:       ["Invalid changeRecord with non-string 'type' property"],
   observe_perform_non_string:    ["Invalid non-string changeType"],
   observe_perform_non_function:  ["Cannot perform non-function"],
   observe_notify_non_notifier:   ["notify called on non-notifier object"],
   observe_global_proxy:          ["%0", " cannot be called on the global proxy object"],
   not_typed_array:               ["this is not a typed array."],
   invalid_argument:              ["invalid_argument"],
   data_view_not_array_buffer:    ["First argument to DataView constructor must be an ArrayBuffer"],
   constructor_not_function:      ["Constructor ", "%0", " requires 'new'"],
   not_a_symbol:                  ["%0", " is not a symbol"],
@@ skipping 1228 matching lines @@
 function SetUpStackOverflowBoilerplate() {
   var boilerplate = MakeRangeError('stack_overflow', []);
 
   %DefineAccessorPropertyUnchecked(
       boilerplate, 'stack', StackTraceGetter, StackTraceSetter, DONT_ENUM);
 
   return boilerplate;
 }
 
 var kStackOverflowBoilerplate = SetUpStackOverflowBoilerplate();