(early draft) Strict mode - throw exception on assignment to read only property.

src/messages.js

Index: src/messages.js
diff --git a/src/messages.js b/src/messages.js
index b7e57aa228ea22f7db50da0fabb2aecd8445e5f7..18d02cd07e41760c789d05efd374284c501fa0fd 100644
--- a/src/messages.js
+++ b/src/messages.js
@@ -226,6 +226,8 @@ function FormatMessage(message) {
       strict_reserved_word:         ["Use of future reserved word in strict mode"],
       strict_delete:                ["Delete of an unqualified identifier in strict mode."],
       strict_delete_property:       ["Cannot delete property '", "%0", "' of ", "%1"],
+      strict_rdonly_property:       ["Cannot assign to read only property '", "%0", "' of ", "%1"],
+      strict_cannot_assign:         ["Cannot assign to read only '", "%0", "' in strict mode"],
     };
   }
   var message_type = %MessageGetType(message);