Throw a more descriptive exception when blocking 'eval' via CSP.

src/messages.js

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 122 matching lines @@
   throw new $Error("Not supported");
 });
 
 
 // Helper functions; called from the runtime system.
 function FormatMessage(message) {
   if (kMessages === 0) {
     var messagesDictionary = [
       // Error
       "cyclic_proto",                 ["Cyclic __proto__ value"],
-      "code_gen_from_strings",        ["Code generation from strings disallowed for this context"],
+      "code_gen_from_strings",        ["%0"],
       // 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 /"],
@@ skipping 1104 matching lines @@
     throw e;
   }
 }
 
 
 InstallFunctions($Error.prototype, DONT_ENUM, ['toString', ErrorToString]);
 
 // Boilerplate for exceptions for stack overflows. Used from
 // Isolate::StackOverflow().
 var kStackOverflowBoilerplate = MakeRangeError('stack_overflow', []);