usb: Add DCHECKs for UsbChooserContext observers

This CL updates UsbChooserContext to require that DeviceObservers
stop observing when the UsbChooserContext is about to be destroyed.

Change-Id: I848bec9c8d5649ed17477f1e9ec767405f13ea29
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3759869
Commit-Queue: Matt Reynolds <[email protected]>
Reviewed-by: Reilly Grant <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1030860}
diff --git a/chrome/browser/usb/usb_chooser_controller.h b/chrome/browser/usb/usb_chooser_controller.h
index 515933e5..e6d9631 100644
--- a/chrome/browser/usb/usb_chooser_controller.h
+++ b/chrome/browser/usb/usb_chooser_controller.h
@@ -55,7 +55,7 @@
   void OnDeviceAdded(const device::mojom::UsbDeviceInfo& device_info) override;
   void OnDeviceRemoved(
       const device::mojom::UsbDeviceInfo& device_info) override;
-  void OnDeviceManagerConnectionError() override;
+  void OnBrowserContextShutdown() override;
 
  private:
   void GotUsbDeviceList(std::vector<device::mojom::UsbDeviceInfoPtr> devices);