Add the c++ code part of bindings2/

sky/engine/bindings2/dart_callback.cc

Index: sky/engine/bindings2/dart_callback.cc
diff --git a/sky/engine/bindings2/dart_callback.cc b/sky/engine/bindings2/dart_callback.cc
new file mode 100644
index 0000000000000000000000000000000000000000..4a20c439226cc471ecf274c163500bd1d1b5f1a5
--- /dev/null
+++ b/sky/engine/bindings2/dart_callback.cc
@@ -0,0 +1,39 @@
+// 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/bindings2/dart_callback.h"
+
+#include "sky/engine/tonic/dart_error.h"
+#include "sky/engine/tonic/dart_state.h"
+
+namespace blink {
+
+DartCallback::DartCallback(DartState* dart_state,
+                           Dart_Handle callback,
+                           Dart_Handle& exception)
+    : callback_(dart_state, callback) {
+  if (!Dart_IsClosure(callback)) {
+    exception = Dart_NewStringFromCString("Callback must be a function");
+    callback_.Clear();
+  }
+}
+
+DartCallback::~DartCallback() {
+}
+
+bool DartCallback::IsIsolateAlive() const {
+  return !!callback_.dart_state();
+}
+
+Dart_Isolate DartCallback::GetIsolate() const {
+  return callback_.dart_state()->isolate();
+}
+
+bool DartCallback::handleEvent(int argc, Dart_Handle* argv) {
+  LogIfError(Dart_InvokeClosure(callback_.value(), argc, argv));
+  return true;
+}
+
+}  // namespace blink