Split the common event classes out to files.

xfa/fwl/core/cfwl_evtscroll.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_FWL_CORE_CFWL_EVTSCROLL_H_
+#define XFA_FWL_CORE_CFWL_EVTSCROLL_H_
+
+#include "xfa/fwl/core/cfwl_event.h"
+
+enum class FWL_SCBCODE {
+  None = 1,
+  Min,
+  Max,
+  PageBackward,
+  PageForward,
+  StepBackward,
+  StepForward,
+  Pos,
+  TrackPos,
+  EndScroll,
+};
+
+class CFWL_EvtScroll : public CFWL_Event {
+ public:
+  CFWL_EvtScroll();
+  ~CFWL_EvtScroll() override;
+
+  CFWL_EventType GetClassID() const override;
+
+  FWL_SCBCODE m_iScrollCode;
+  FX_FLOAT m_fPos;
+  bool* m_pRet;
+};
+
+#endif  // XFA_FWL_CORE_CFWL_EVTSCROLL_H_