Add missing include guards in Cocoa code.

chrome/browser/ui/cocoa/location_bar/autocomplete_text_field_cell.h

Index: chrome/browser/ui/cocoa/location_bar/autocomplete_text_field_cell.h
diff --git a/chrome/browser/ui/cocoa/location_bar/autocomplete_text_field_cell.h b/chrome/browser/ui/cocoa/location_bar/autocomplete_text_field_cell.h
index 1e3ca73d1bfa0fee02c5c88fc034bb314033e123..bc1e235c894c152f887f8c4b79bd85216284b750 100644
--- a/chrome/browser/ui/cocoa/location_bar/autocomplete_text_field_cell.h
+++ b/chrome/browser/ui/cocoa/location_bar/autocomplete_text_field_cell.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_LOCATION_BAR_AUTOCOMPLETE_TEXT_FIELD_CELL_H_
+#define CHROME_BROWSER_UI_COCOA_LOCATION_BAR_AUTOCOMPLETE_TEXT_FIELD_CELL_H_
+
 #include <vector>
 
 #import <Cocoa/Cocoa.h>
@@ -145,3 +148,5 @@ class LocationBarDecoration;
 - (const std::vector<LocationBarDecoration*>&)mouseTrackingDecorations;
 
 @end
+
+#endif  // CHROME_BROWSER_UI_COCOA_LOCATION_BAR_AUTOCOMPLETE_TEXT_FIELD_CELL_H_