Use override in more classes in fpdfsdk/

fpdfsdk/include/formfiller/FFL_CheckBox.h

Index: fpdfsdk/include/formfiller/FFL_CheckBox.h
diff --git a/fpdfsdk/include/formfiller/FFL_CheckBox.h b/fpdfsdk/include/formfiller/FFL_CheckBox.h
index 0ac7170a1661ec92798ff9d05867a5a6e8d6dbbe..27af16be5a01c6b1570b37d856b37564b552477c 100644
--- a/fpdfsdk/include/formfiller/FFL_CheckBox.h
+++ b/fpdfsdk/include/formfiller/FFL_CheckBox.h
@@ -12,22 +12,21 @@
 class CFFL_CheckBox : public CFFL_Button {
  public:
   CFFL_CheckBox(CPDFDoc_Environment* pApp, CPDFSDK_Widget* pWidget);
-  virtual ~CFFL_CheckBox();
-
-  virtual CPWL_Wnd* NewPDFWindow(const PWL_CREATEPARAM& cp,
-                                 CPDFSDK_PageView* pPageView);
-
-  virtual FX_BOOL OnKeyDown(CPDFSDK_Annot* pAnnot,
-                            FX_UINT nKeyCode,
-                            FX_UINT nFlags);
-  virtual FX_BOOL OnChar(CPDFSDK_Annot* pAnnot, FX_UINT nChar, FX_UINT nFlags);
-  virtual FX_BOOL OnLButtonUp(CPDFSDK_PageView* pPageView,
-                              CPDFSDK_Annot* pAnnot,
-                              FX_UINT nFlags,
-                              const CPDF_Point& point);
-
-  virtual FX_BOOL IsDataChanged(CPDFSDK_PageView* pPageView);
-  virtual void SaveData(CPDFSDK_PageView* pPageView);
+  ~CFFL_CheckBox() override;
+
+  // CFFL_Button
+  CPWL_Wnd* NewPDFWindow(const PWL_CREATEPARAM& cp,
+                         CPDFSDK_PageView* pPageView) override;
+  FX_BOOL OnKeyDown(CPDFSDK_Annot* pAnnot,
+                    FX_UINT nKeyCode,
+                    FX_UINT nFlags) override;
+  FX_BOOL OnChar(CPDFSDK_Annot* pAnnot, FX_UINT nChar, FX_UINT nFlags) override;
+  FX_BOOL OnLButtonUp(CPDFSDK_PageView* pPageView,
+                      CPDFSDK_Annot* pAnnot,
+                      FX_UINT nFlags,
+                      const CPDF_Point& point) override;
+  FX_BOOL IsDataChanged(CPDFSDK_PageView* pPageView) override;
+  void SaveData(CPDFSDK_PageView* pPageView) override;
 };
 
 #endif  // FPDFSDK_INCLUDE_FORMFILLER_FFL_CHECKBOX_H_