content: Cleanup class/struct forward declarations

chrome/browser/ui/webui/signin/inline_login_handler.h

 // Copyright 2013 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_WEBUI_SIGNIN_INLINE_LOGIN_HANDLER_H_
 #define CHROME_BROWSER_UI_WEBUI_SIGNIN_INLINE_LOGIN_HANDLER_H_
 
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "content/public/browser/web_ui_message_handler.h"
 
+namespace base {
+class DictionaryValue;
+}
+
 namespace signin_metrics {
 enum class AccessPoint;
 }
 
 // The base class handler for the inline login WebUI.
 class InlineLoginHandler : public content::WebUIMessageHandler {
  public:
   InlineLoginHandler();
   ~InlineLoginHandler() override;
 
@@ skipping 37 matching lines @@
 
   virtual void SetExtraInitParams(base::DictionaryValue& params) {}
   virtual void CompleteLogin(const base::ListValue* args) = 0;
 
   base::WeakPtrFactory<InlineLoginHandler> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(InlineLoginHandler);
 };
 
 #endif  // CHROME_BROWSER_UI_WEBUI_SIGNIN_INLINE_LOGIN_HANDLER_H_