[epiphany] prefs-dialog: Fix build failure with sync disabled

[Michael Catanzaro <mcatanzaro src gnome org>]

commit b138da5c6fdd289dde713e0bb59653444007b212
Author: Michael Catanzaro <mcatanzaro gnome org>
Date:   Tue Jan 3 09:12:20 2017 -0600

    prefs-dialog: Fix build failure with sync disabled

 src/prefs-dialog.c |    9 ++++++---
 1 files changed, 6 insertions(+), 3 deletions(-)
---
diff --git a/src/prefs-dialog.c b/src/prefs-dialog.c
index b49dff1..a89bc51 100644
--- a/src/prefs-dialog.c
+++ b/src/prefs-dialog.c
@@ -36,9 +36,6 @@
 #include "ephy-session.h"
 #include "ephy-settings.h"
 #include "ephy-shell.h"
-#include "ephy-sync-crypto.h"
-#include "ephy-sync-secret.h"
-#include "ephy-sync-service.h"
 #include "clear-data-dialog.h"
 #include "cookies-dialog.h"
 #include "languages.h"
@@ -50,6 +47,12 @@
 #include <json-glib/json-glib.h>
 #include <string.h>
 
+#ifdef ENABLE_SYNC
+#include "ephy-sync-crypto.h"
+#include "ephy-sync-secret.h"
+#include "ephy-sync-service.h"
+#endif
+
 #define DOWNLOAD_BUTTON_WIDTH   8
 #define FXA_IFRAME_URL "https://accounts.firefox.com/signin?service=sync&context=fx_ios_v1";