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

printing/backend/print_backend.cc

Index: printing/backend/print_backend.cc
diff --git a/printing/backend/print_backend.cc b/printing/backend/print_backend.cc
index f17983778d76a8998f02e801dc98d6e993210e3a..6d472e044b7385937d10f7b24f85d6bcaa2f1f25 100644
--- a/printing/backend/print_backend.cc
+++ b/printing/backend/print_backend.cc
@@ -4,6 +4,10 @@
 
 #include "printing/backend/print_backend.h"
 
+namespace {
+bool g_native_cups_enabled = false;
+}  // namespace
+
 namespace printing {
 
 PrinterBasicInfo::PrinterBasicInfo()
@@ -40,4 +44,14 @@ PrinterCapsAndDefaults::~PrinterCapsAndDefaults() {}
 
 PrintBackend::~PrintBackend() {}
 
+// static
+bool PrintBackend::GetNativeCupsEnabled() {
+  return g_native_cups_enabled;
+}
+
+// static
+void PrintBackend::SetNativeCupsEnabled(bool enabled) {
+  g_native_cups_enabled = enabled;
+}
+
 }  // namespace printing