Add a missing include that broke the M59 beta build.

chrome/browser/ui/find_bar/find_bar_controller.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_UI_FIND_BAR_FIND_BAR_CONTROLLER_H_
 #define CHROME_BROWSER_UI_FIND_BAR_FIND_BAR_CONTROLLER_H_
 
 #include <memory>
 
 #include "base/macros.h"
+#include "base/strings/string16.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 
 class FindBar;
 
 namespace content {
 class WebContents;
 }
 
 namespace gfx {
@@ skipping 81 matching lines @@
   // Used to keep track of whether the user has been notified that the find came
   // up empty. A single find session can result in multiple final updates, if
   // the document contents change dynamically. It's a nuisance to notify the
   // user more than once that a search came up empty, however.
   base::string16 alerted_search_;
 
   DISALLOW_COPY_AND_ASSIGN(FindBarController);
 };
 
 #endif  // CHROME_BROWSER_UI_FIND_BAR_FIND_BAR_CONTROLLER_H_