Fix missing callback chaining in UsbService.

chrome/browser/usb/usb_service.cc

Index: chrome/browser/usb/usb_service.cc
diff --git a/chrome/browser/usb/usb_service.cc b/chrome/browser/usb/usb_service.cc
index 21e2e33dbdf202b66050b8d04480316aaf2117a4..fcad23d94fc78ee555ac23a2cacbb330f056096c 100644
--- a/chrome/browser/usb/usb_service.cc
+++ b/chrome/browser/usb/usb_service.cc
@@ -70,30 +70,38 @@ void UsbService::Cleanup() {
 
 void UsbService::FindDevices(const uint16 vendor_id,
                              const uint16 product_id,
-                             vector<scoped_refptr<UsbDevice> >* devices) {
+                             vector<scoped_refptr<UsbDevice> >* devices,
+                             const base::Callback<void()>& callback) {
   DCHECK(event_handler_) << "FindDevices called after event handler stopped.";
 #if defined(OS_CHROMEOS)
   chromeos::PermissionBrokerClient* client =
       chromeos::DBusThreadManager::Get()->GetPermissionBrokerClient();
   DCHECK(client) << "Could not get permission broker client.";
-  if (!client)
+  if (!client) {
+    callback.Run();
     return;
+  }
+
   client->RequestUsbAccess(vendor_id,
                            product_id,
                            base::Bind(&UsbService::FindDevicesImpl,
                                       base::Unretained(this),
                                       vendor_id,
                                       product_id,
-                                      devices));
+                                      devices,
+                                      callback));
 #else
-  FindDevicesImpl(vendor_id, product_id, devices, true);
+  FindDevicesImpl(vendor_id, product_id, devices, callback, true);
 #endif  // defined(OS_CHROMEOS)
 }
 
 void UsbService::FindDevicesImpl(const uint16 vendor_id,
                                  const uint16 product_id,
                                  vector<scoped_refptr<UsbDevice> >* devices,
+                                 const base::Callback<void()>& callback,
                                  bool success) {
+  base::ScopedClosureRunner run_callback(callback);
+
   devices->clear();
 
   // If the permission broker was unable to obtain permission for the specified