Don't attempt to forward declare StringPiece.

content/shell/shell.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 CONTENT_SHELL_SHELL_H_
 #define CONTENT_SHELL_SHELL_H_
 
 #pragma once
 
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/string_piece.h"
 #include "content/browser/tab_contents/tab_contents_delegate.h"
 #include "ui/gfx/native_widget_types.h"
 
 class GURL;
 class SiteInstance;
 class TabContents;
 
-namespace base {
-class StringPiece;
-}
-
 namespace content {
 
 class BrowserContext;
 
 // This represents one window of the Content Shell, i.e. all the UI including
 // buttons and url bar, as well as the web content area.
 class Shell : public TabContentsDelegate {
  public:
   virtual ~Shell();
 
@@ skipping 75 matching lines @@
 #endif
 
   // A container of all the open windows. We use a vector so we can keep track
   // of ordering.
   static std::vector<Shell*> windows_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_SHELL_SHELL_H_