Add WillDestroyUsbService method to UsbService::Observer interface.

This method will assist objects that observe the UsbService in removing
their observers before the UsbService is shut down.

Review URL: https://codereview.chromium.org/1324093004

Cr-Commit-Position: refs/heads/master@{#347978}

3 files changed, 10 insertions, 1 deletions

diff --git a/device/devices_app/usb/device_manager_impl.cc b/device/devices_app/usb/device_manager_impl.cc
index f438460..559edf6 100644
--- a/device/devices_app/usb/device_manager_impl.cc
+++ b/device/devices_app/usb/device_manager_impl.cc
@@ -153,6 +153,8 @@ class DeviceManagerImpl::ServiceThreadHelper
                               device->guid()));
   }
 
+  void WillDestroyUsbService() override { observer_.RemoveAll(); }
+
   // base::MessageLoop::DestructionObserver
   void WillDestroyCurrentMessageLoop() override { delete this; }
 
diff --git a/device/usb/usb_service.cc b/device/usb/usb_service.cc
index ef6763a..de9716f 100644
--- a/device/usb/usb_service.cc
+++ b/device/usb/usb_service.cc
@@ -24,13 +24,17 @@ void UsbService::Observer::OnDeviceRemovedCleanup(
     scoped_refptr<UsbDevice> device) {
 }
 
+void UsbService::Observer::WillDestroyUsbService() {}
+
 // static
 scoped_ptr<UsbService> UsbService::Create(
     scoped_refptr<base::SequencedTaskRunner> blocking_task_runner) {
   return make_scoped_ptr(new UsbServiceImpl(blocking_task_runner));
 }
 
-UsbService::~UsbService() {}
+UsbService::~UsbService() {
+  FOR_EACH_OBSERVER(Observer, observer_list_, WillDestroyUsbService());
+}
 
 UsbService::UsbService() {}
 
diff --git a/device/usb/usb_service.h b/device/usb/usb_service.h
index dbb837f..519feb6 100644
--- a/device/usb/usb_service.h
+++ b/device/usb/usb_service.h
@@ -42,6 +42,9 @@ class UsbService : public base::NonThreadSafe {
     // For observers that need to process device removal after others have run.
     // Should not depend on any other service's knowledge of connected devices.
     virtual void OnDeviceRemovedCleanup(scoped_refptr<UsbDevice> device);
+
+    // Notifies the observer that the UsbService it depends on is shutting down.
+    virtual void WillDestroyUsbService();
   };
 
   // The file task runner reference is used for blocking I/O operations.