Improve error reporting for duplicate object template properties.

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"],
   generator_running:             ["Generator is already running"],
   generator_finished:            ["Generator has already finished"],
   // TypeError
   unexpected_token:              ["Unexpected token ", "%0"],
   unexpected_token_number:       ["Unexpected number"],
   unexpected_token_string:       ["Unexpected string"],
   unexpected_token_identifier:   ["Unexpected identifier"],
   unexpected_reserved:           ["Unexpected reserved word"],
   unexpected_strict_reserved:    ["Unexpected strict mode reserved word"],
   unexpected_eos:                ["Unexpected end of input"],
   malformed_regexp:              ["Invalid regular expression: /", "%0", "/: ", "%1"],
   unterminated_regexp:           ["Invalid regular expression: missing /"],
   regexp_flags:                  ["Cannot supply flags when constructing one RegExp from another"],
   incompatible_method_receiver:  ["Method ", "%0", " called on incompatible receiver ", "%1"],
   multiple_defaults_in_switch:   ["More than one default clause in switch statement"],
   newline_after_throw:           ["Illegal newline after throw"],
   label_redeclaration:           ["Label '", "%0", "' has already been declared"],
   var_redeclaration:             ["Identifier '", "%0", "' has already been declared"],
+  duplicate_template_property:   ["Object template has duplicate property '", "%0", "'"],
   no_catch_or_finally:           ["Missing catch or finally after try"],
   unknown_label:                 ["Undefined label '", "%0", "'"],
   uncaught_exception:            ["Uncaught ", "%0"],
   stack_trace:                   ["Stack Trace:\n", "%0"],
   called_non_callable:           ["%0", " is not a function"],
   undefined_method:              ["Object ", "%1", " has no method '", "%0", "'"],
   property_not_function:         ["Property '", "%0", "' of object ", "%1", " is not a function"],
   cannot_convert_to_primitive:   ["Cannot convert object to primitive value"],
   not_constructor:               ["%0", " is not a constructor"],
   not_defined:                   ["%0", " is not defined"],
@@ skipping 1299 matching lines @@
     return result;
   };
 
   %DefineAccessorPropertyUnchecked(
       boilerplate, 'stack', getter, setter, DONT_ENUM);
 
   return boilerplate;
 }
 
 var kStackOverflowBoilerplate = SetUpStackOverflowBoilerplate();