Add a UsbService::Observer function for cleanup actions.

This patch adds an additional function to the UsbService::Observer
interface that should be used to perform cleanup operations when a USB
device is disconnected. This is separate from the OnDeviceRemoved
function so that implementations of that function, which may depend on
other subsystems' knowledge of a connected device, can run before any
cleanup actions have taken place.

A browsertest for the chrome.usb.getUserSelectedDevices is included
which demonstrates the need for this 2-phase event handling.

BUG=452298

Review URL: https://codereview.chromium.org/891853002

Cr-Commit-Position: refs/heads/master@{#314973}

1 files changed, 5 insertions, 0 deletions

diff --git a/device/usb/usb_service.cc b/device/usb/usb_service.cc
index 70f054d..3faa3e5 100644
--- a/device/usb/usb_service.cc
+++ b/device/usb/usb_service.cc
@@ -44,6 +44,10 @@ void UsbService::Observer::OnDeviceAdded(scoped_refptr<UsbDevice> device) {
 void UsbService::Observer::OnDeviceRemoved(scoped_refptr<UsbDevice> device) {
 }
 
+void UsbService::Observer::OnDeviceRemovedCleanup(
+    scoped_refptr<UsbDevice> device) {
+}
+
 // static
 UsbService* UsbService::GetInstance(
     scoped_refptr<base::SingleThreadTaskRunner> ui_task_runner) {
@@ -85,6 +89,7 @@ void UsbService::NotifyDeviceAdded(scoped_refptr<UsbDevice> device) {
 void UsbService::NotifyDeviceRemoved(scoped_refptr<UsbDevice> device) {
   DCHECK(CalledOnValidThread());
   FOR_EACH_OBSERVER(Observer, observer_list_, OnDeviceRemoved(device));
+  FOR_EACH_OBSERVER(Observer, observer_list_, OnDeviceRemovedCleanup(device));
 }
 
 }  // namespace device