Move NSWindow.allowsAutomaticWindowTabbing forward declaration to the right place.

base/mac/sdk_forward_declarations.h

Index: base/mac/sdk_forward_declarations.h
diff --git a/base/mac/sdk_forward_declarations.h b/base/mac/sdk_forward_declarations.h
index cd42240736db5b7673dc807dcc0e92d5367ee74f..29e35218249f28b999e718e9cf2fb80beafa5420 100644
--- a/base/mac/sdk_forward_declarations.h
+++ b/base/mac/sdk_forward_declarations.h
@@ -38,10 +38,6 @@
 @protocol CALayerDelegate
 @end
 
-@interface NSWindow (SierraSDK)
-@property(class) BOOL allowsAutomaticWindowTabbing;
-@end
-
 #endif  // MAC_OS_X_VERSION_10_12
 
 #if !defined(MAC_OS_X_VERSION_10_11) || \
@@ -244,6 +240,17 @@ BASE_EXPORT extern NSString* const NSAppearanceNameVibrantLight;
 
 #endif  // MAC_OS_X_VERSION_10_10
 
+// Once Chrome no longer supports OSX 10.11, everything within this
+// preprocessor block can be removed.
+#if !defined(MAC_OS_X_VERSION_10_12) || \
+    MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_12
+
+@interface NSWindow (SierraSDK)
+@property(class) BOOL allowsAutomaticWindowTabbing;
+@end
+
+#endif  // MAC_OS_X_VERSION_10_12
+
 // ----------------------------------------------------------------------------
 // The symbol for kCWSSIDDidChangeNotification is available in the
 // CoreWLAN.framework for OSX versions 10.6 through 10.10. The symbol is not