[Mac] Build fix when using newer SDK

ui/base/cocoa/touch_bar_forward_declarations.h

Index: ui/base/cocoa/touch_bar_forward_declarations.h
diff --git a/ui/base/cocoa/touch_bar_forward_declarations.h b/ui/base/cocoa/touch_bar_forward_declarations.h
index ce03c6aae01fa624634aa51b475f948a18b9a7be..34390b7239799a6a8bc404fca203c1348e3e6a2b 100644
--- a/ui/base/cocoa/touch_bar_forward_declarations.h
+++ b/ui/base/cocoa/touch_bar_forward_declarations.h
@@ -11,10 +11,10 @@
 
 #include "ui/base/ui_base_export.h"
 
-#if !defined(MAC_OS_X_VERSION_10_12_1)
-
 #pragma clang assume_nonnull begin
 
+#if !defined(MAC_OS_X_VERSION_10_12_1)
+
 @class NSTouchBar, NSTouchBarItem;
 @protocol NSTouchBarDelegate;