diff -r 000000000000 -r 6474c204b198 security/sandbox/chromium/base/sequence_checker.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/security/sandbox/chromium/base/sequence_checker.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,68 @@
+// Copyright (c) 2012 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 BASE_SEQUENCE_CHECKER_H_
+#define BASE_SEQUENCE_CHECKER_H_
+
+#include "base/memory/ref_counted.h"
+
+// See comments for the similar block in thread_checker.h.
+#if (!defined(NDEBUG) || defined(DCHECK_ALWAYS_ON))
+#define ENABLE_SEQUENCE_CHECKER 1
+#else
+#define ENABLE_SEQUENCE_CHECKER 0
+#endif
+
+#if ENABLE_SEQUENCE_CHECKER
+#include "base/sequence_checker_impl.h"
+#endif
+
+namespace base {
+
+class SequencedTaskRunner;
+
+// Do nothing implementation, for use in release mode.
+//
+// Note: You should almost always use the SequenceChecker class to get
+// the right version for your build configuration.
+class SequenceCheckerDoNothing {
+ public:
+  bool CalledOnValidSequencedThread() const {
+    return true;
+  }
+
+  void DetachFromSequence() {}
+};
+
+// SequenceChecker is a helper class used to help verify that some
+// methods of a class are called in sequence -- that is, called from
+// the same SequencedTaskRunner. It is a generalization of
+// ThreadChecker; see comments in sequence_checker_impl.h for details.
+//
+// Example:
+// class MyClass {
+//  public:
+//   void Foo() {
+//     DCHECK(sequence_checker_.CalledOnValidSequence());
+//     ... (do stuff) ...
+//   }
+//
+//  private:
+//   SequenceChecker sequence_checker_;
+// }
+//
+// In Release mode, CalledOnValidSequence will always return true.
+#if ENABLE_SEQUENCE_CHECKER
+class SequenceChecker : public SequenceCheckerImpl {
+};
+#else
+class SequenceChecker : public SequenceCheckerDoNothing {
+};
+#endif  // ENABLE_SEQUENCE_CHECKER
+
+#undef ENABLE_SEQUENCE_CHECKER
+
+}  // namespace base
+
+#endif  // BASE_SEQUENCE_CHECKER_H_