Move printing defines to buildflag system.

printing/BUILD.gn

Index: printing/BUILD.gn
diff --git a/printing/BUILD.gn b/printing/BUILD.gn
index 421ae56bb660adeca586a8b49658e67f397b7092..cd2ccdc9ec52225249483866b0763092f9afadd4 100644
--- a/printing/BUILD.gn
+++ b/printing/BUILD.gn
@@ -5,6 +5,7 @@
 import("//build/config/features.gni")
 import("//build/config/sysroot.gni")
 import("//build/config/ui.gni")
+import("//printing/features/features.gni")
 import("//testing/test.gni")
 if (is_mac) {
   import("//build/config/mac/mac_sdk.gni")
@@ -74,6 +75,9 @@ component("printing") {
   cflags = []
   defines = [ "PRINTING_IMPLEMENTATION" ]
 
+  public_deps = [
+    "//printing/features",
+  ]
   deps = [
     "//base",
     "//base:i18n",