Add the c++ code part of bindings2/

sky/engine/bindings2/dart_callback.h

Index: sky/engine/bindings2/dart_callback.h
diff --git a/sky/engine/bindings2/dart_callback.h b/sky/engine/bindings2/dart_callback.h
new file mode 100644
index 0000000000000000000000000000000000000000..78c54a636c12fff9c7b183f776b31bc926b7ef5c
--- /dev/null
+++ b/sky/engine/bindings2/dart_callback.h
@@ -0,0 +1,30 @@
+// 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.
+
+#ifndef SKY_ENGINE_BINDINGS2_DART_CALLBACK_H_
+#define SKY_ENGINE_BINDINGS2_DART_CALLBACK_H_
+
+#include "dart/runtime/include/dart_api.h"
+#include "sky/engine/tonic/dart_persistent_value.h"
+
+namespace blink {
+
+class DartCallback {
+ public:
+  DartCallback(DartState* dart_state,
+               Dart_Handle callback,
+               Dart_Handle& exception);
+  ~DartCallback();
+
+  bool handleEvent(int argc, Dart_Handle* argv);
+
+  bool IsIsolateAlive() const;
+  Dart_Isolate GetIsolate() const;
+
+ private:
+  DartPersistentValue callback_;
+};
+}
+
+#endif  // SKY_ENGINE_BINDINGS2_DART_CALLBACK_H_