Make code compile with clang_use_chrome_plugin (part V)chromium/2770

This change mainly contains files in xfa/fxfa directory.
This is part of the efforts to make PDFium code compilable
by Clang chromium style plugins.

The changes are mainly the following:
-- move inline constructor/destructor of complex class/struct out-of-line;
-- add constructor/destructor of complex class/struct if not
 explicitly defined;
-- add explicit out-of-line copy constructor when needed;
-- move inline virtual functions out-of-line;
-- Properly mark virtual functions with 'override';
-- some minor cleanups;

BUG=pdfium:469

Review-Url: https://codereview.chromium.org/2071683002

1 files changed, 1 insertions, 1 deletions

diff --git a/xfa/fxfa/app/xfa_ffsubform.h b/xfa/fxfa/app/xfa_ffsubform.h
index fd3da98670..6607edf23b 100644
--- a/xfa/fxfa/app/xfa_ffsubform.h
+++ b/xfa/fxfa/app/xfa_ffsubform.h
@@ -13,7 +13,7 @@
 class CXFA_FFSubForm : public CXFA_FFWidget {
  public:
   CXFA_FFSubForm(CXFA_FFPageView* pPageView, CXFA_WidgetAcc* pDataAcc);
-  virtual ~CXFA_FFSubForm();
+  ~CXFA_FFSubForm() override;
 };
 
 #endif  // XFA_FXFA_APP_XFA_FFSUBFORM_H_