Add missed files in Windows GN build for printing.

printing/BUILD.gn

 # Copyright 2014 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.
 
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 if (is_mac) {
   import("//build/config/mac/mac_sdk.gni")
 }
 if (is_android) {
@@ skipping 90 matching lines @@
   }
 
   if (is_win) {
     # PRINT_BACKEND_AVAILABLE disables the default dummy implementation of the
     # print backend and enables a custom implementation instead.
     defines += [ "PRINT_BACKEND_AVAILABLE" ]
     sources += [
       "backend/win_helper.cc",
       "backend/win_helper.h",
       "backend/print_backend_win.cc",
+      "printing_context_system_dialog_win.cc",
+      "printing_context_system_dialog_win.h",
       "printing_context_win.cc",
       "printing_context_win.h",
     ]
   }
 
   if (is_chromeos) {
     sources += [
       "printing_context_no_system_dialog.cc",
       "printing_context_no_system_dialog.h",
     ]
@@ skipping 117 matching lines @@
   }
 
   # GYP: //printing/printing.gyp:printing_java
   android_library("printing_java") {
     deps = [
       "//base:base_java",
     ]
     DEPRECATED_java_in_dir = "android/java/src"
   }
 }