Destroy DeviceImpl when the underlying UsbDevice is disconnected.

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 <stdint.h>
 
 #include <string>
 #include <vector>
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
+#include "base/observer_list.h"
 #include "base/strings/string16.h"
 #include "device/usb/usb_descriptors.h"
 #include "url/gurl.h"
 
 namespace device {
 
 class UsbDeviceHandle;
 struct WebUsbAllowedOrigins;
 
 // A UsbDevice object represents a detected USB device, providing basic
 // information about it. Methods other than simple property accessors must be
 // called from the thread on which this object was created. For further
 // manipulation of the device, a UsbDeviceHandle must be created from Open()
 // method.
 class UsbDevice : public base::RefCountedThreadSafe<UsbDevice> {
  public:
   using OpenCallback = base::Callback<void(scoped_refptr<UsbDeviceHandle>)>;
   using ResultCallback = base::Callback<void(bool success)>;
 
+  // This observer interface should be used by objects that need only be
+  // notified about the removal of a particular device as it is more efficient
+  // than registering a large number of observers with UsbService::AddObserver.
+  class Observer {
+   public:
+    virtual ~Observer();
+
+    // This method is called when the UsbService that created this object
+    // detects that the device has been disconnected from the host.
+    virtual void OnDeviceRemoved(scoped_refptr<UsbDevice> device);
+  };
+
   // A unique identifier which remains stable for the lifetime of this device
   // object (i.e., until the device is unplugged or the USB service dies.)
   const std::string& guid() const { return guid_; }
 
   // Accessors to basic information.
   uint16_t vendor_id() const { return vendor_id_; }
   uint16_t product_id() const { return product_id_; }
   const base::string16& manufacturer_string() const {
     return manufacturer_string_;
   }
@@ skipping 12 matching lines @@
   // functions are no-ops and always return true.
   virtual void CheckUsbAccess(const ResultCallback& callback);
 
   // Creates a UsbDeviceHandle for further manipulation.
   virtual void Open(const OpenCallback& callback) = 0;
 
   // Gets the UsbConfigDescriptor for the active device configuration or nullptr
   // if the device is unconfigured.
   virtual const UsbConfigDescriptor* GetActiveConfiguration() = 0;
 
+  void AddObserver(Observer* observer);
+  void RemoveObserver(Observer* observer);
+
  protected:
+  friend class UsbService;
+
   UsbDevice(uint16_t vendor_id,
             uint16_t product_id,
             const base::string16& manufacturer_string,
             const base::string16& product_string,
             const base::string16& serial_number);
   virtual ~UsbDevice();
 
+  void NotifyDeviceRemoved();
+
   // These members must be mutable by subclasses as necessary during device
   // enumeration. To preserve the thread safety of this object they must remain
   // constant afterwards.
   base::string16 manufacturer_string_;
   base::string16 product_string_;
   base::string16 serial_number_;
   scoped_ptr<WebUsbAllowedOrigins> webusb_allowed_origins_;
   GURL webusb_landing_page_;
 
   // All of the device's configuration descriptors.
   std::vector<UsbConfigDescriptor> configurations_;
 
  private:
   friend class base::RefCountedThreadSafe<UsbDevice>;
 
   const std::string guid_;
   const uint16_t vendor_id_;
   const uint16_t product_id_;
 
+  base::ObserverList<Observer, true> observer_list_;
+
   DISALLOW_COPY_AND_ASSIGN(UsbDevice);
 };
 
 }  // namespace device
 
 #endif  // DEVICE_USB_USB_DEVICE_H_