Split the common event classes out to files.

xfa/fwl/core/cfwl_evtsizechanged.h

Index: xfa/fwl/core/cfwl_evtsizechanged.h
diff --git a/xfa/fwl/core/cfwl_evtsizechanged.h b/xfa/fwl/core/cfwl_evtsizechanged.h
new file mode 100644
index 0000000000000000000000000000000000000000..fe2dc6f5e5d9d79cada9e0782263a7a628041600
--- /dev/null
+++ b/xfa/fwl/core/cfwl_evtsizechanged.h
@@ -0,0 +1,24 @@
+// 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_EVTSIZECHANGED_H_
+#define XFA_FWL_CORE_CFWL_EVTSIZECHANGED_H_
+
+#include "xfa/fwl/core/cfwl_event.h"
+
+class CFWL_EvtSizeChanged : public CFWL_Event {
+ public:
+  CFWL_EvtSizeChanged();
+  ~CFWL_EvtSizeChanged() override;
+
+  CFWL_EventType GetClassID() const override;
+
+  IFWL_Widget* m_pWidget;
+  CFX_RectF m_rtOld;
+  CFX_RectF m_rtNew;
+};
+
+#endif  // XFA_FWL_CORE_CFWL_EVTSIZECHANGED_H_