Make header include guards great again

runtime/vm/datastream.h

Index: runtime/vm/datastream.h
diff --git a/runtime/vm/datastream.h b/runtime/vm/datastream.h
index 58452a07f64afc36b617ed0a8cfbfe36d0caa8f3..ca235356aedc31ef42fe2f7afc87ce05c1a0e24b 100644
--- a/runtime/vm/datastream.h
+++ b/runtime/vm/datastream.h
@@ -2,8 +2,8 @@
 // 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 VM_DATASTREAM_H_
-#define VM_DATASTREAM_H_
+#ifndef RUNTIME_VM_DATASTREAM_H_
+#define RUNTIME_VM_DATASTREAM_H_
 
 #include "platform/assert.h"
 #include "platform/utils.h"
@@ -478,4 +478,4 @@ class WriteStream : public ValueObject {
 
 }  // namespace dart
 
-#endif  // VM_DATASTREAM_H_
+#endif  // RUNTIME_VM_DATASTREAM_H_