Add missing include guards in Cocoa code.

chrome/browser/ui/cocoa/download/download_show_all_button.h

Index: chrome/browser/ui/cocoa/download/download_show_all_button.h
diff --git a/chrome/browser/ui/cocoa/download/download_show_all_button.h b/chrome/browser/ui/cocoa/download/download_show_all_button.h
index 6e1afe1b98d30c1cfcf819bb07b4b888bb851ed0..e2f5734fdb70237ecec790c612c5f2388bf29681 100644
--- a/chrome/browser/ui/cocoa/download/download_show_all_button.h
+++ b/chrome/browser/ui/cocoa/download/download_show_all_button.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_DOWNLOAD_DOWNLOAD_SHOW_ALL_BUTTON_H_
+#define CHROME_BROWSER_UI_COCOA_DOWNLOAD_DOWNLOAD_SHOW_ALL_BUTTON_H_
+
 #import <Cocoa/Cocoa.h>
 
 #import "chrome/browser/ui/cocoa/themed_window.h"
@@ -10,3 +13,5 @@
 // -sizeToFit logic.
 @interface DownloadShowAllButton : NSButton<ThemedWindowDrawing>
 @end
+
+#endif  // CHROME_BROWSER_UI_COCOA_DOWNLOAD_DOWNLOAD_SHOW_ALL_BUTTON_H_