Change IFWL_Widget to store a single delegate.

xfa/fxfa/app/cxfa_fffielddelegate.h

+// Copyright 2016 PDFium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
+
+#ifndef XFA_FXFA_APP_CXFA_FFFIELDDELEGATE_H_
+#define XFA_FXFA_APP_CXFA_FFFIELDDELEGATE_H_
+
+#include "core/fxcrt/fx_coordinates.h"
+#include "xfa/fwl/core/cfwl_event.h"
+#include "xfa/fwl/core/cfwl_message.h"
+#include "xfa/fwl/core/ifwl_widgetdelegate.h"
+#include "xfa/fxfa/app/xfa_fffield.h"
+#include "xfa/fxfa/xfa_ffwidget.h"
+#include "xfa/fxgraphics/cfx_graphics.h"
+
+class CXFA_FFFieldDelegate : public IFWL_WidgetDelegate {
+ public:
+  CXFA_FFFieldDelegate(std::unique_ptr<IFWL_WidgetDelegate> pDelegate,
+                       CXFA_FFField* const pWidget);
+  ~CXFA_FFFieldDelegate() override;
+
+  // IFWL_WidgetDelegate
+  void OnProcessMessage(CFWL_Message* pMessage) override;
+  void OnProcessEvent(CFWL_Event* pEvent) override;
+  void OnDrawWidget(CFX_Graphics* pGraphics,
+                    const CFX_Matrix* pMatrix) override;
+
+ protected:
+  std::unique_ptr<IFWL_WidgetDelegate> m_pDelegate;
+  CXFA_FFWidget* const m_pWidget;  // Not owned.
+};
+
+#endif  // XFA_FXFA_APP_CXFA_FFFIELDDELEGATE_H_