[Mac] Build fix when using newer SDK

ui/base/cocoa/touch_bar_forward_declarations.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_BASE_COCOA_TOUCH_BAR_FORWARD_DECLARATIONS_H_
 #define UI_BASE_COCOA_TOUCH_BAR_FORWARD_DECLARATIONS_H_
 
 // Once Chrome no longer supports OSX 10.12.0, this file can be deleted.
 #import <AppKit/AppKit.h>
 #import <Foundation/Foundation.h>
 
 #include "ui/base/ui_base_export.h"
 
+#pragma clang assume_nonnull begin
+
 #if !defined(MAC_OS_X_VERSION_10_12_1)
 
-#pragma clang assume_nonnull begin
-
 @class NSTouchBar, NSTouchBarItem;
 @protocol NSTouchBarDelegate;
 
 typedef float NSTouchBarItemPriority;
 static const NSTouchBarItemPriority NSTouchBarItemPriorityHigh = 1000;
 static const NSTouchBarItemPriority NSTouchBarItemPriorityNormal = 0;
 static const NSTouchBarItemPriority NSTouchBarItemPriorityLow = -1000;
 
 typedef NSString* NSTouchBarItemIdentifier;
 typedef NSString* NSTouchBarCustomizationIdentifier;
@@ skipping 86 matching lines @@
 #if !defined(MAC_OS_X_VERSION_10_12_1) || \
     MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_12_1
 UI_BASE_EXPORT extern NSString* const NSTouchBarItemIdentifierFixedSpaceSmall;
 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_