Change IFWL_Widget to store a single delegate.

xfa/fxfa/app/cxfa_ffcheckbuttondelegate.h

+// Copyright 2016 PDFium Authors. All rights reserved.

[Tom Sepez, 2016/11/01 20:54:04]

rather than adding all these tiny files, how about we first convert
IFWL_WidgetDelegate to IFWL_Widget::Delegate nested classes. Then
this can go in the same file as the class the delegate refers back to.

It feels kinda weird for a class to own the delegate handed to it, since it
must outlive it.  In that case, you'd save a lot of trouble by making it
never own the delegate instead of always owning it.

[dsinclair, 2016/11/01 20:58:10]

Changing IFWL_WidgetDelegate to IFWL_Widget::Delegate is a much larger change as
there are a whole bunch of delegates that live in the IFWL_* hierarchy. Seems
like it would be better as two steps. I can move these back into their parent
classes as public/private inner classes depending on inheritance if that's
desired. I'd prefer to do IFWL_Widget::Delegate as a separate change afterwards.

Making which class never own the delegate, the IFWL_Widget? In that case, you'd
make the creating widget own the delegate passed to IFWL_Widget?

+// 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_FFCHECKBUTTONDELEGATE_H_
+#define XFA_FXFA_APP_CXFA_FFCHECKBUTTONDELEGATE_H_
+
+#include "core/fxcrt/fx_coordinates.h"
+#include "xfa/fwl/core/cfwl_event.h"
+#include "xfa/fwl/core/cfwl_message.h"
+#include "xfa/fxfa/app/cxfa_fffielddelegate.h"
+#include "xfa/fxfa/app/xfa_ffcheckbutton.h"
+#include "xfa/fxfa/xfa_ffwidget.h"
+#include "xfa/fxgraphics/cfx_graphics.h"
+
+class CXFA_FFCheckButtonDelegate : public CXFA_FFFieldDelegate {
+ public:
+  CXFA_FFCheckButtonDelegate(std::unique_ptr<IFWL_WidgetDelegate> pDelegate,
+                             CXFA_FFCheckButton* const pWidget);
+  ~CXFA_FFCheckButtonDelegate() override;
+
+  // CXFA_FFFieldDelegate.
+  void OnProcessMessage(CFWL_Message* pMessage) override;
+  void OnProcessEvent(CFWL_Event* pEvent) override;
+  void OnDrawWidget(CFX_Graphics* pGraphics,
+                    const CFX_Matrix* pMatrix) override;
+};
+
+#endif  // XFA_FXFA_APP_CXFA_FFCHECKBUTTONDELEGATE_H_