Add installer::SetupSingleton.

chrome/installer/setup/setup_singleton.h

Index: chrome/installer/setup/setup_singleton.h
diff --git a/chrome/installer/setup/setup_singleton.h b/chrome/installer/setup/setup_singleton.h
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index 0000000000000000000000000000000000000000..03874fd9fe38939c8ffbbb6f232478e7a106a0c1
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+++ b/chrome/installer/setup/setup_singleton.h
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+// Copyright 2016 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 CHROME_INSTALLER_SETUP_SETUP_SINGLETON_H_
+#define CHROME_INSTALLER_SETUP_SETUP_SINGLETON_H_
+
+#include <memory>
+
+#include "base/macros.h"
+#include "base/synchronization/waitable_event.h"
+#include "base/win/scoped_handle.h"
+
+namespace base {
+class FilePath;
+class TimeDelta;
+}
+
+namespace installer {
+
+class InstallerState;
+
+// Any modification to a Chrome installation should be done within the scope of
+// a SetupSingleton. There can be only one active SetupSingleton per Chrome
+// installation at a time.
+class SetupSingleton {
+ public:
+  // Acquires the exclusive right to modify the Chrome installation described by
+  // |installer_state| (installation directory and associated registry keys).
+  // May block.
+  explicit SetupSingleton(const InstallerState& installer_state);
+
+  // Acquires the exclusive right to modify the Chrome installation located in
+  // |install_dir| (installation directory and associated registry keys).
+  // |system_install| indicates whether this is a system-level installation. May
+  // block.
+  SetupSingleton(const base::FilePath& install_dir, bool system_install);
+
+  // Releases the exclusive right to modifiy the Chrome installation.
+  ~SetupSingleton();
+
+  // Waits until |max_time| has passed or another SetupSingleton is instantiated
+  // with the same Chrome installation as this SetupSingleton (possibly in
+  // another process).
+
+  // Returns true if another SetupSingleton is instantiated with the same Chrome
+  // installation as this SetupSingleton. In such a case, this SetupSingleton
+  // should be deleted as soon as possible to unblock the other SetupSingleton.
+  // Returns false otherwise.
+  bool Wait(const base::TimeDelta& max_time);
+
+ private:
+  // A mutex that must be held to modify the Chrome installation directory.
+  base::win::ScopedHandle setup_mutex_;
+
+  // An event signaled to ask the owner of |setup_mutex_| to release it as soon
+  // as possible.
+  std::unique_ptr<base::WaitableEvent> exit_event_;
+
+  DISALLOW_COPY_AND_ASSIGN(SetupSingleton);
+};
+
+}  // namespace installer
+
+#endif  // CHROME_INSTALLER_SETUP_SETUP_SINGLETON_H_