Move enable_pdf to a buildflag header.

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("//pdf/features.gni")
 import("//printing/features/features.gni")
 import("//testing/test.gni")
 if (is_mac) {
   import("//build/config/mac/mac_sdk.gni")
 }
 if (is_android) {
   import("//build/config/android/rules.gni")
 }
 
+if ((enable_basic_printing && is_win) || enable_print_preview) {
+  # Windows basic printing or print preview requires pdf enabled.
+  assert(enable_pdf,
+         "Windows basic printing or print preview needs pdf: " +
+             "set enable_pdf=true.")
+}
+
 component("printing") {
   sources = [
     "backend/print_backend.cc",
     "backend/print_backend.h",
     "backend/print_backend_consts.cc",
     "backend/print_backend_consts.h",
     "backend/print_backend_dummy.cc",
     "backend/printing_info_win.cc",
     "backend/printing_info_win.h",
     "emf_win.cc",
@@ skipping 283 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",
     ]
   }
 }