[CrOS Tether] Make BluetoothThrottler a singleton which can be easily shared between EasyUnlock and…

components/cryptauth/bluetooth_throttler_impl.h

 // Copyright 2015 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 COMPONENTS_CRYPTAUTH_BLUETOOTH_THROTTLER_IMPL_H_
 #define COMPONENTS_CRYPTAUTH_BLUETOOTH_THROTTLER_IMPL_H_
 
 #include <memory>
 #include <set>
 
 #include "base/macros.h"
+#include "base/memory/singleton.h"
 #include "base/time/time.h"
 #include "components/cryptauth/bluetooth_throttler.h"
 #include "components/cryptauth/connection_observer.h"
 
 namespace base {
 class TickClock;
 }
 
 namespace cryptauth {
 
 class Connection;
 
 // This class throttles repeated connection attempts to the same device. This
 // throttling is necessary to prevent a kernel race condition when connecting
 // before the previous connection fully closes, putting the connection in a
 // corrupted, and unrecoverable state. http://crbug.com/345232
 class BluetoothThrottlerImpl : public BluetoothThrottler,
                                public ConnectionObserver {
  public:
-  // Creates a throttler for connections to a remote device, using the |clock|
-  // as a time source.
-  explicit BluetoothThrottlerImpl(std::unique_ptr<base::TickClock> clock);
+  static BluetoothThrottlerImpl* GetInstance();

[Tim Song, 2017/04/06 23:38:12]

I would put this singleton getter in bluetooth_throttler.h rather than in the
impl.

   ~BluetoothThrottlerImpl() override;
 
   // BluetoothThrottler:
   base::TimeDelta GetDelay() const override;
   void OnConnection(Connection* connection) override;
 
  protected:
+  // Creates a throttler for connections to a remote device, using the |clock|
+  // as a time source.
+  explicit BluetoothThrottlerImpl(std::unique_ptr<base::TickClock> clock);
+
   // Returns the duration to wait, after disconnecting, before reattempting a
   // connection to the remote device. Exposed for testing.
   base::TimeDelta GetCooldownTimeDelta() const;
 
  private:
+  friend struct base::DefaultSingletonTraits<BluetoothThrottlerImpl>;
+
+  BluetoothThrottlerImpl();
+
   // ConnectionObserver:
   void OnConnectionStatusChanged(Connection* connection,
                                  Connection::Status old_status,
                                  Connection::Status new_status) override;
 
   // Tracks the last seen disconnect time for the |remote_device_|.
   base::TimeTicks last_disconnect_time_;
 
   // The time source.
   std::unique_ptr<base::TickClock> clock_;
 
   // The currently connected connections.
   // Each connection is stored as a weak reference, which is safe because |this|
   // instance is registered as an observer, and will unregister when the
   // connection disconnects, which is guaranteed to occur before the connection
   // is destroyed.
   std::set<Connection*> connections_;
 
   DISALLOW_COPY_AND_ASSIGN(BluetoothThrottlerImpl);
 };
 
 }  // namespace cryptauth
 
 #endif  // COMPONENTS_CRYPTAUTH_BLUETOOTH_THROTTLER_IMPL_H_