Add browser tests for USB device add/remove events.

device/usb/BUILD.gn

 # Copyright (c) 2013 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.
 
 assert(!is_android && !is_ios)
 
 source_ids = "//third_party/usb_ids/usb.ids"
 generated_ids = "$target_gen_dir/usb_ids_gen.cc"
 
 source_set("usb") {
   sources = [
     "usb_context.cc",
     "usb_context.h",
     "usb_descriptors.cc",
     "usb_descriptors.h",
     "usb_device_impl.cc",
     "usb_device_impl.h",
     "usb_device.h",
     "usb_device_filter.cc",
     "usb_device_filter.h",
     "usb_device_handle_impl.cc",
     "usb_device_handle_impl.h",
     "usb_device_handle.h",
     "usb_error.cc",
     "usb_error.h",
     "usb_ids.cc",
     "usb_ids.h",
+    "usb_service.cc",
     "usb_service.h",
     "usb_service_impl.cc",
+    "usb_service_impl.h",
     generated_ids,
   ]
 
   deps = [
     ":usb_device_ids",
     "//base",
     "//base/third_party/dynamic_annotations",
     "//net",
     "//third_party/libusb",
   ]
@@ skipping 14 matching lines @@
   args = [
     "-i",
     rebase_path(source_ids, root_build_dir),
     "-o",
     rebase_path(generated_ids, root_build_dir),
   ]
 
   # Only the device_usb target can depend on us.
   visibility = [ ":usb" ]
 }