Don't attempt to forward declare StringPiece.

chrome/browser/extensions/user_script_master.h

 // Copyright (c) 2011 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_EXTENSIONS_USER_SCRIPT_MASTER_H_
 #define CHROME_BROWSER_EXTENSIONS_USER_SCRIPT_MASTER_H_
 #pragma once
 
 #include <map>
 #include <string>
 
 #include "base/compiler_specific.h"
 #include "base/file_path.h"
 #include "base/gtest_prod_util.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/shared_memory.h"
+#include "base/string_piece.h"
 #include "chrome/browser/extensions/extension_info_map.h"
 #include "chrome/common/extensions/extension_messages.h"
 #include "chrome/common/extensions/extension_set.h"
 #include "chrome/common/extensions/user_script.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 
-namespace base {
-class StringPiece;
-}
-
 namespace content {
 class RenderProcessHost;
 }
 
 class Profile;
 
 typedef std::map<std::string, ExtensionSet::ExtensionPathAndDefaultLocale>
     ExtensionsInfo;
 
 // Manages a segment of shared memory that contains the user scripts the user
@@ skipping 126 matching lines @@
   // finishes.  This boolean tracks whether another load is pending.
   bool pending_load_;
 
   // The profile for which the scripts managed here are installed.
   Profile* profile_;
 
   DISALLOW_COPY_AND_ASSIGN(UserScriptMaster);
 };
 
 #endif  // CHROME_BROWSER_EXTENSIONS_USER_SCRIPT_MASTER_H_