[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..07a54b21220625ae0168e29795b1af267a5ae3e4 100644
--- a/ui/base/cocoa/touch_bar_forward_declarations.h
+++ b/ui/base/cocoa/touch_bar_forward_declarations.h
@@ -93,6 +93,8 @@ typedef NSString* NSTouchBarCustomizationIdentifier;
                makeItemForIdentifier:(NSTouchBarItemIdentifier)identifier;
 @end
 
+#pragma clang assume_nonnull end

[spqchan, 2017/04/21 20:23:39]

Instead of putting this here, it makes more sense to move 

#pragma clang assume_nonnull begin

to before L14

+
 #elif MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_12_1
 
 // When compiling against the 10.12.1 SDK or later, just provide forward
@@ -118,6 +120,5 @@ UI_BASE_EXPORT extern NSString* const NSTouchBarItemIdentifierFlexibleSpace;
 #endif  // MAC_OS_X_VERSION_10_12_1
 }  // extern "C"
 
-#pragma clang assume_nonnull end
 
 #endif  // UI_BASE_COCOA_TOUCH_BAR_FORWARD_DECLARATIONS_H_