Add missing include guards in Cocoa code.

chrome/browser/ui/cocoa/fullscreen_window.h

Index: chrome/browser/ui/cocoa/fullscreen_window.h
diff --git a/chrome/browser/ui/cocoa/fullscreen_window.h b/chrome/browser/ui/cocoa/fullscreen_window.h
index 12be00d93168f3366711acab6bafa8b0970e89ed..840aee532e0664905e1bbf7c88c9338b083b2c1b 100644
--- a/chrome/browser/ui/cocoa/fullscreen_window.h
+++ b/chrome/browser/ui/cocoa/fullscreen_window.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_FULLSCREEN_WINDOW_H_
+#define CHROME_BROWSER_UI_COCOA_FULLSCREEN_WINDOW_H_
+
 #include <Cocoa/Cocoa.h>
 #import "chrome/browser/ui/cocoa/chrome_browser_window.h"
 
@@ -17,3 +20,5 @@
 - (id)initForScreen:(NSScreen*)screen;
 
 @end
+
+#endif  // CHROME_BROWSER_UI_COCOA_FULLSCREEN_WINDOW_H_