ParentNode#appendChild(null) shouldn't crash

sky/engine/tonic/dart_exception_factory.cc

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "sky/engine/config.h"
+#include "sky/engine/tonic/dart_exception_factory.h"
+
+#include "sky/engine/tonic/dart_converter.h"
+#include "sky/engine/tonic/dart_builtin.h"
+
+namespace blink {
+
+DartExceptionFactory::DartExceptionFactory(DartState* dart_state)
+    : dart_state_(dart_state) {
+}
+
+DartExceptionFactory::~DartExceptionFactory() {
+}
+
+Dart_Handle DartExceptionFactory::CreateException(const String& class_name,
+                                                  const String& message) {
+  if (core_library_.is_empty()) {
+    Dart_Handle library = DartBuiltin::LookupLibrary("dart:core");
+    core_library_.Set(dart_state_, library);
+  }
+
+  Dart_Handle exception_class = Dart_GetType(
+      core_library_.value(), StringToDart(dart_state_, class_name), 0, 0);
+  Dart_Handle message_handle = StringToDart(dart_state_, message);
+  Dart_Handle empty_string = Dart_NewStringFromCString("");

[esprehn, 2015/02/17 18:06:53]

Do we want a shared per isolate empty string? Exceptions are probably rare, so
this is fine I suppose.

[abarth-chromium, 2015/02/17 18:14:05]

It looks like Dart_NewStringFromCString("") is relatively expensive (e.g., it
really does allocate storage in the heap).  It would be pretty easy to add an
entry for the empty string to the DartStringCache, but I'm not sure its worth
doing for this use case.  Let's do it if the topic comes up again.

+  return Dart_New(exception_class, empty_string, 1, &message_handle);
+}
+
+}  // namespace blink