Make code compile with clang_use_chrome_plugin (part III)

This change contains files in xfa/fxbarcode 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/2067903002
diff --git a/xfa/fxbarcode/datamatrix/BC_SymbolInfo.h b/xfa/fxbarcode/datamatrix/BC_SymbolInfo.h
index 64270dd..96196da 100644
--- a/xfa/fxbarcode/datamatrix/BC_SymbolInfo.h
+++ b/xfa/fxbarcode/datamatrix/BC_SymbolInfo.h
@@ -21,7 +21,8 @@
                  int32_t matrixWidth,
                  int32_t matrixHeight,
                  int32_t dataRegions);
-  virtual ~CBC_SymbolInfo();
+  ~CBC_SymbolInfo() override;
+
   static void Initialize();
   static void Finalize();
   static void overrideSymbolSet(CBC_SymbolInfo* override);