Fix (nearly all) IWYU in fpdfskd/include/javascript/ headers.

fpdfsdk/include/javascript/JS_EventHandler.h

 // 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
 
 #ifndef _JS_EVENTHANDLER_H_
 #define _JS_EVENTHANDLER_H_
 
+#include "../../../core/include/fxcrt/fx_string.h"
+#include "../../../core/include/fxcrt/fx_system.h"
+
 class CJS_Context;
+class CPDFSDK_Annot;
+class CPDFSDK_Document;
+class CPDF_Bookmark;
+class CPDF_FormField;
 class Field;
 
 enum JS_EVENT_T
 {
         JET_UNKNOWN,
         JET_APP_INIT,
         JET_DOC_OPEN,
         JET_DOC_WILLPRINT,
         JET_DOC_DIDPRINT,
         JET_DOC_WILLSAVE,
@@ skipping 137 matching lines @@
         FX_BOOL                                 m_bRcDu;
 
         CPDFSDK_Document*               m_pSourceDoc;
         CPDF_Bookmark*                  m_pTargetBookMark;
         CPDFSDK_Document*               m_pTargetDoc;
         CPDFSDK_Annot*                  m_pTargetAnnot;
 };
 
 #endif //_JS_EVENTHANDLER_H_