Add missing include guards in Cocoa code.

chrome/browser/ui/cocoa/bookmarks/bookmark_bar_folder_view.h

Index: chrome/browser/ui/cocoa/bookmarks/bookmark_bar_folder_view.h
diff --git a/chrome/browser/ui/cocoa/bookmarks/bookmark_bar_folder_view.h b/chrome/browser/ui/cocoa/bookmarks/bookmark_bar_folder_view.h
index 48ef52003bf709d35a78e47d8f1b6f8409bb6cab..95008d5d9ee34b786249602b6d29bf0923a18ea9 100644
--- a/chrome/browser/ui/cocoa/bookmarks/bookmark_bar_folder_view.h
+++ b/chrome/browser/ui/cocoa/bookmarks/bookmark_bar_folder_view.h
@@ -2,6 +2,9 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#ifndef CHROME_BROWSER_UI_COCOA_BOOKMARKS_BOOKMARK_BAR_FOLDER_VIEW_H_
+#define CHROME_BROWSER_UI_COCOA_BOOKMARKS_BOOKMARK_BAR_FOLDER_VIEW_H_
+
 #import <Cocoa/Cocoa.h>
 
 #import "base/mac/scoped_nsobject.h"
@@ -21,3 +24,5 @@
   base::scoped_nsobject<NSBox> dropIndicator_;
 }
 @end
+
+#endif  // CHROME_BROWSER_UI_COCOA_BOOKMARKS_BOOKMARK_BAR_FOLDER_VIEW_H_