Split the common event classes out to files.

xfa/fwl/core/ifwl_pushbutton.cpp

 // Copyright 2014 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
 
 #include "xfa/fwl/core/ifwl_pushbutton.h"
 
 #include "third_party/base/ptr_util.h"
 #include "xfa/fde/tto/fde_textout.h"
+#include "xfa/fwl/core/cfwl_evtclick.h"
+#include "xfa/fwl/core/cfwl_evtmouse.h"
 #include "xfa/fwl/core/cfwl_msgkey.h"
 #include "xfa/fwl/core/cfwl_msgmouse.h"
 #include "xfa/fwl/core/cfwl_themebackground.h"
 #include "xfa/fwl/core/cfwl_themetext.h"
 #include "xfa/fwl/core/fwl_noteimp.h"
 #include "xfa/fwl/core/ifwl_pushbutton.h"
 #include "xfa/fwl/core/ifwl_themeprovider.h"
 
 IFWL_PushButton::IFWL_PushButton(
     const IFWL_App* app,
@@ skipping 342 matching lines @@
     CFWL_EvtClick wmClick;
     wmClick.m_pSrcTarget = this;
     DispatchEvent(&wmClick);
     return;
   }
   if (pMsg->m_dwKeyCode != FWL_VKEY_Tab)
     return;
 
   DispatchKeyEvent(pMsg);
 }