Add a service to track devices selected by the user.

device/usb/usb_device.h

 // Copyright 2014 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 DEVICE_USB_USB_DEVICE_H_
 #define DEVICE_USB_USB_DEVICE_H_
 
 #include "base/basictypes.h"
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
+#include "base/observer_list.h"
 
 namespace device {
 
 class UsbDeviceHandle;
 struct UsbConfigDescriptor;
 
 // A UsbDevice object represents a detected USB device, providing basic
 // information about it. For further manipulation of the device, a
 // UsbDeviceHandle must be created from Open() method.
 class UsbDevice : public base::RefCountedThreadSafe<UsbDevice> {
  public:
+  class Observer {
+   public:
+    virtual void OnDisconnect(scoped_refptr<UsbDevice> device) = 0;
+  };
+
   // Accessors to basic information.
   uint16 vendor_id() const { return vendor_id_; }
   uint16 product_id() const { return product_id_; }
   uint32 unique_id() const { return unique_id_; }
 
 #if defined(OS_CHROMEOS)
   // On ChromeOS, if an interface of a claimed device is not claimed, the
   // permission broker can change the owner of the device so that the unclaimed
   // interfaces can be used. If this argument is missing, permission broker will
   // not be used and this method fails if the device is claimed.
   virtual void RequestUsbAccess(
       int interface_id,
       const base::Callback<void(bool success)>& callback) = 0;
 #endif  // OS_CHROMEOS
 
   // Creates a UsbDeviceHandle for further manipulation.
   // Blocking method. Must be called on FILE thread.
   virtual scoped_refptr<UsbDeviceHandle> Open() = 0;
 
   // Explicitly closes a device handle. This method will be automatically called
   // by the destructor of a UsbDeviceHandle as well.
   // Closing a closed handle is a safe
   // Blocking method. Must be called on FILE thread.
   virtual bool Close(scoped_refptr<UsbDeviceHandle> handle) = 0;
 
   // Gets the UsbConfigDescriptor for the active device configuration.
   // Blocking method. Must be called on FILE thread.
   virtual const UsbConfigDescriptor& GetConfiguration() = 0;
 
+  void AddObserver(Observer* obs) { observer_list_.AddObserver(obs); }
+  void RemoveObserver(Observer* obs) { observer_list_.RemoveObserver(obs); }
+
  protected:
-  UsbDevice(uint16 vendor_id, uint16 product_id, uint32 unique_id)
-      : vendor_id_(vendor_id), product_id_(product_id), unique_id_(unique_id) {}
+  UsbDevice(uint16 vendor_id, uint16 product_id, uint32 unique_id);
+  virtual ~UsbDevice();
 
-  virtual ~UsbDevice() {}
+  void NotifyDisconnect();
 
  private:
   friend class base::RefCountedThreadSafe<UsbDevice>;
 
   const uint16 vendor_id_;
   const uint16 product_id_;
   const uint32 unique_id_;
 
+  ObserverList<Observer> observer_list_;
+
   DISALLOW_COPY_AND_ASSIGN(UsbDevice);
 };
 
 }  // namespace device
 
 #endif  // DEVICE_USB_USB_DEVICE_H_