Rename CancellationFlag to AtomicFlag.

base/synchronization/atomic_flag.h

Index: base/synchronization/atomic_flag.h
diff --git a/base/synchronization/atomic_flag.h b/base/synchronization/atomic_flag.h
new file mode 100644
index 0000000000000000000000000000000000000000..07bf38b3e6d0c221e9586fb84bf75ee309d6cdc1
--- /dev/null
+++ b/base/synchronization/atomic_flag.h
@@ -0,0 +1,43 @@
+// Copyright (c) 2011 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_SYNCHRONIZATION_ATOMIC_FLAG_H_
+#define BASE_SYNCHRONIZATION_ATOMIC_FLAG_H_
+
+#include "base/atomicops.h"
+#include "base/base_export.h"
+#include "base/macros.h"
+#include "base/threading/thread_checker.h"
+
+namespace base {
+
+// A flag that can safely be set from one thread and read from other threads.
+//
+// This class IS NOT intended for synchronization between threads.
+class BASE_EXPORT AtomicFlag {
+ public:
+  AtomicFlag();
+  ~AtomicFlag() = default;
+
+  // Set the flag. May only be called on the thread which created the object.
+  void Set();
+
+  // Returns true iff the flag was set.
+  bool IsSet() const;
+
+  // For subtle reasons that may be different on different architectures, a
+  // different thread testing IsSet() may erroneously read 'true' after this

[danakj, 2016/07/20 19:21:01]

Really? But it's using Release_Store. Is this still true?

[fdoray, 2016/07/21 13:08:33]

Talked with the author of https://codereview.chromium.org/949293002/ - it seems
that it's only unsafe because of this:

if (flag.IsSet()) {
  // Can't assume that the flag is still set here
  // because of UnsafeResetForTesting().
}

+  // method has been called.
+  void UnsafeResetForTesting();
+
+ private:
+  base::subtle::Atomic32 flag_ = false;
+  ThreadChecker thread_checker_;
+
+  DISALLOW_COPY_AND_ASSIGN(AtomicFlag);
+};
+
+}  // namespace base
+
+#endif  // BASE_SYNCHRONIZATION_ATOMIC_FLAG_H_