Add test case for custom error's toString.

test/cctest/test-api.cc

Index: test/cctest/test-api.cc
diff --git a/test/cctest/test-api.cc b/test/cctest/test-api.cc
index 8db3fcb438d9743f58845f4844526172d1a12331..eae682a0979c1404f2fa680e455ca9ff356046e5 100644
--- a/test/cctest/test-api.cc
+++ b/test/cctest/test-api.cc
@@ -3056,6 +3056,32 @@ TEST(APIThrowMessageOverwrittenToString) {
 }
 
 
+static void check_custom_error_message(
+    v8::Handle<v8::Message> message,
+    v8::Handle<v8::Value> data) {
+  const char* uncaught_error = "Uncaught MyError toString";
+  CHECK(message->Get()->Equals(v8_str(uncaught_error)));
+}
+
+
+TEST(CustomErrorToString) {
+  v8::HandleScope scope;
+  v8::V8::AddMessageListener(check_custom_error_message);
+  LocalContext context;
+  CompileRun(
+    "function MyError(name, message) {                   "
+    "  this.name = name;                                 "
+    "  this.message = message;                           "
+    "}                                                   "
+    "MyError.prototype = Object.create(Error.prototype); "
+    "MyError.prototype.toString = function() {           "
+    "  return 'MyError toString';                        "
+    "};                                                  "
+    "throw new MyError('my name', 'my message');         ");
+  v8::V8::RemoveMessageListeners(check_custom_error_message);
+}
+
+
 static void receive_message(v8::Handle<v8::Message> message,
                             v8::Handle<v8::Value> data) {
   message->Get();