Add embedded_dart_io source_set for Sky

runtime/bin/embedded_dart_io.h

Index: runtime/bin/embedded_dart_io.h
diff --git a/runtime/bin/embedded_dart_io.h b/runtime/bin/embedded_dart_io.h
new file mode 100644
index 0000000000000000000000000000000000000000..e19b21ac8d1f968421795a789351ec94d6bf530e
--- /dev/null
+++ b/runtime/bin/embedded_dart_io.h
@@ -0,0 +1,17 @@
+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#ifndef BIN_EMBEDDED_DART_IO_H_
+#define BIN_EMBEDDED_DART_IO_H_
+
+namespace dart {
+namespace bin {
+
+// Bootstraps 'dart:io'.
+void BootstrapDartIo();
+
+}  // namespace bin
+}  // namespace dart
+
+#endif  // BIN_EMBEDDED_DART_IO_H_