Remove include only fwl.h and IWYU.

xfa/include/fwl/core/fwl_target.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 XFA_INCLUDE_FWL_CORE_FWL_TARGET_H_
 #define XFA_INCLUDE_FWL_CORE_FWL_TARGET_H_
 
 #include "core/include/fxcrt/fx_basic.h"
+#include "xfa/include/fwl/core/fwl_error.h"
 
 // FWL contains three parallel inheritance hierarchies, which reference each
 // other via pointers as follows:
 //
 //                                           m_pImpl
 //      (nonesuch)              IFWL_Target ----------> CFWL_TargetImp
 //                                   |                       |
 //                                   A                       A
 //                   m_pIface        |                       |
 //      CFWL_Widget ----------> IFWL_Widget             CFWL_WidgetImp
@@ skipping 21 matching lines @@
   CFWL_TargetImp* GetImpl() const { return m_pImpl; }
 
  protected:
   void SetImpl(CFWL_TargetImp* pImpl) { m_pImpl = pImpl; }
 
  private:
   CFWL_TargetImp* m_pImpl;
 };
 
 #endif  // XFA_INCLUDE_FWL_CORE_FWL_TARGET_H_