Remove include only fwl.h and IWYU.

xfa/include/fwl/lightwidget/picturebox.h

Index: xfa/include/fwl/lightwidget/picturebox.h
diff --git a/xfa/include/fwl/lightwidget/picturebox.h b/xfa/include/fwl/lightwidget/picturebox.h
index bd994ac1e8032142a5b15eabfc6a56a25c57a628..5a2117624162bc828a0f6cc8043ccc71d789c894 100644
--- a/xfa/include/fwl/lightwidget/picturebox.h
+++ b/xfa/include/fwl/lightwidget/picturebox.h
@@ -7,11 +7,10 @@
 #ifndef XFA_INCLUDE_FWL_LIGHTWIDGET_PICTUREBOX_H_
 #define XFA_INCLUDE_FWL_LIGHTWIDGET_PICTUREBOX_H_
 
-class CFWL_Widget;
-class CFWL_WidgetProperties;
-class IFWL_PictureBoxDP;
-class CFWL_PictureBox;
-class CFWL_PictureBoxDP;
+#include "xfa/include/fwl/basewidget/fwl_picturebox.h"
+#include "xfa/include/fwl/core/fwl_error.h"
+#include "xfa/include/fwl/lightwidget/widget.h"
+
 class CFWL_PictureBox : public CFWL_Widget {
  public:
   static CFWL_PictureBox* Create();