Do not eagerly convert exception to string when creating a message object

test/cctest/test-api.cc

 // 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 4914 matching lines @@
       "  this.name = 'MyError';                            "
       "  this.message = msg;                               "
       "}                                                   "
       "MyError.prototype = Object.create(Error.prototype); "
       "throw new MyError('my message');                    ");
 
   v8::V8::RemoveMessageListeners(check_custom_error_message);
 }
 
 
+static void check_custom_rethrowing_message(v8::Handle<v8::Message> message,
+                                            v8::Handle<v8::Value> data) {
+  const char* uncaught_error = "Uncaught exception";
+  CHECK(message->Get()->Equals(v8_str(uncaught_error)));
+}
+
+
+TEST(CustomErrorRethrowsOnToString) {
+  LocalContext context;
+  v8::HandleScope scope(context->GetIsolate());
+  v8::V8::AddMessageListener(check_custom_rethrowing_message);
+
+  CompileRun(
+      "var e = { toString: function() { throw e; } };"
+      "try { throw e; } finally {}");
+
+  v8::V8::RemoveMessageListeners(check_custom_rethrowing_message);
+}
+
+
 static void receive_message(v8::Handle<v8::Message> message,
                             v8::Handle<v8::Value> data) {
   message->Get();
   message_received = true;
 }
 
 
 TEST(APIThrowMessage) {
   message_received = false;
   v8::Isolate* isolate = CcTest::isolate();
@@ skipping 16130 matching lines @@
   // add the testExtraShouldReturnFive export
   v8::Local<v8::Object> exports = env->GetExtrasExportsObject();
 
   auto func =
       exports->Get(v8_str("testExtraShouldReturnFive")).As<v8::Function>();
   auto undefined = v8::Undefined(isolate);
   auto result = func->Call(undefined, 0, {}).As<v8::Number>();
 
   CHECK(result->Value() == 5.0);
 }