Add unordered_set

Change-Id: I2f8a7dba75b8cf26e23a350720920ba2e694e840
diff --git a/src/unordered_set.h b/src/unordered_set.h
new file mode 100644
index 0000000..18ebaac
--- /dev/null
+++ b/src/unordered_set.h
@@ -0,0 +1,12 @@
+// Copyright 2011 Google Inc. All Rights Reserved.
+
+#ifndef ART_SRC_CLASS_UNORDERED_SET_H_
+#define ART_SRC_CLASS_UNORDERED_SET_H_
+
+#ifdef __ANDROID__
+#include <unordered_set>
+#else
+#include <tr1/unordered_set>
+#endif
+
+#endif  // ART_SRC_CLASS_UNORDERED_SET_H_