Bug 1567094 - Fix non-unified build in nsCSSRendering.cpp. r=jrmuizel

Differential Revision: https://phabricator.services.mozilla.com/D41932

--HG--
extra : moz-landing-system : lando

layout/painting/nsCSSRendering.cpp

@@ -13,6 +13,7 @@
 #include "mozilla/ArrayUtils.h"
 #include "mozilla/ComputedStyle.h"
 #include "mozilla/DebugOnly.h"
+#include "mozilla/StaticPrefs_layout.h"
 #include "mozilla/gfx/2D.h"
 #include "mozilla/gfx/Helpers.h"
 #include "mozilla/gfx/PathHelpers.h"