Enable the cups backend when --enable-native-cups is specified.

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/sysroot.gni")
 import("//build/config/ui.gni")
 import("//testing/test.gni")
 if (is_mac) {
   import("//build/config/mac/mac_sdk.gni")
@@ skipping 105 matching lines @@
       "backend/print_backend_win.cc",
       "backend/win_helper.cc",
       "backend/win_helper.h",
       "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",
-    ]
-  }
-
   if (use_cups) {
     configs += [ ":cups" ]
 
     if (is_linux) {
       # rebase_path does not accept an empty string
       if (use_sysroot) {
         cups_sysroot = rebase_path(sysroot)
       } else {
         cups_sysroot = ""
       }
@@ skipping 27 matching lines @@
     }
 
     # PRINT_BACKEND_AVAILABLE disables the default dummy implementation
     # of the print backend and enables a custom implementation instead.
     defines += [ "PRINT_BACKEND_AVAILABLE" ]
 
     sources += [
       "backend/cups_helper.cc",
       "backend/cups_helper.h",
       "backend/print_backend_cups.cc",
+      "backend/print_backend_cups.h",
     ]
   }
 
   if (is_chromeos) {
-    # PRINT_BACKEND_AVAILABLE disables the default dummy implementation
-    # of the print backend and enables a custom implementation instead.
     defines += [ "PRINT_BACKEND_AVAILABLE" ]
 
-    sources += [ "backend/print_backend_chromeos.cc" ]
+    sources += [
+      "backend/print_backend_chromeos.cc",
+      "printing_context_no_system_dialog.cc",
+      "printing_context_no_system_dialog.h",
+    ]
   } else if (is_linux) {  # Non-ChromeOS Linux.
     sources += [
       "printing_context_linux.cc",
       "printing_context_linux.h",
     ]
   }
 
   if (is_android) {
     sources += [
       "printing_context_android.cc",
@@ skipping 89 matching lines @@
       "android/java/src/org/chromium/printing/PrintManagerDelegate.java",
       "android/java/src/org/chromium/printing/PrintManagerDelegateImpl.java",
       "android/java/src/org/chromium/printing/Printable.java",
       "android/java/src/org/chromium/printing/PrintingContext.java",
       "android/java/src/org/chromium/printing/PrintingContextInterface.java",
       "android/java/src/org/chromium/printing/PrintingController.java",
       "android/java/src/org/chromium/printing/PrintingControllerImpl.java",
     ]
   }
 }