Extract //device/usb mocks so that they can be shared.

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") {
@@ skipping 33 matching lines @@
   ]
 
   if (is_linux) {
     deps += [ "//device/udev_linux" ]
   }
   if (is_chromeos) {
     deps += [ "//chromeos" ]
   }
 }
 
+source_set("mocks") {
+  testonly = true
+
+  sources = [
+    "mock_usb_device.cc",
+    "mock_usb_device.h",
+    "mock_usb_device_handle.cc",
+    "mock_usb_device_handle.h",
+    "mock_usb_service.cc",
+    "mock_usb_service.h",
+  ]
+
+  deps = [
+    "//base",
+    "//testing/gmock",
+    ":usb",
+  ]
+}
+
 action("usb_device_ids") {
   script = "//device/usb/tools/usb_ids.py"
   inputs = [
     source_ids,
   ]
   outputs = [
     generated_ids,
   ]
   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" ]
 }