Add cloud_print to the GN build.

cloud_print/virtual_driver/win/BUILD.gn

 # Copyright 2015 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.
 
-executable("clear_system_cache") {
-  testonly = true
+assert(is_win)
 
+source_set("win") {
   sources = [
-    "clear_system_cache_main.cc",
+    "virtual_driver_consts.cc",
+    "virtual_driver_consts.h",
+    "virtual_driver_helpers.cc",
+    "virtual_driver_helpers.h",
   ]
 
   deps = [
     "//base",
-    "//base/test:test_support",
-    "//build/config/sanitizers:deps",
+    "//cloud_print/common",
   ]
 }