components: Cleanup class/struct fwd declarations

chrome/browser/ui/cocoa/javascript_app_modal_dialog_cocoa.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_COCOA_JAVASCRIPT_APP_MODAL_DIALOG_COCOA_H_
 #define CHROME_BROWSER_UI_COCOA_JAVASCRIPT_APP_MODAL_DIALOG_COCOA_H_
 
 #include <memory>
 
 #include "base/logging.h"
 #include "base/mac/scoped_nsobject.h"
 #include "base/macros.h"
 #include "components/app_modal/native_app_modal_dialog.h"
 
 class AppModalDialogHelper;
 
+namespace app_modal {
+class JavaScriptAppModalDialog;
+}
+
 #if __OBJC__
 @class NSAlert;
 @class JavaScriptAppModalDialogHelper;
 #else
 class NSAlert;
 class JavaScriptAppModalDialogHelper;
 #endif
 
 class JavaScriptAppModalDialogCocoa : public app_modal::NativeAppModalDialog {
  public:
@@ skipping 23 matching lines @@
 
   // Created in the constructor and destroyed in the destructor.
   base::scoped_nsobject<JavaScriptAppModalDialogHelper> helper_;
 
   bool is_showing_;
 
   DISALLOW_COPY_AND_ASSIGN(JavaScriptAppModalDialogCocoa);
 };
 
 #endif  // CHROME_BROWSER_UI_COCOA_JAVASCRIPT_APP_MODAL_DIALOG_COCOA_H_