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/cbc_ean13.cpp b/xfa/fxbarcode/cbc_ean13.cpp
index 589af5b..0725083 100644
--- a/xfa/fxbarcode/cbc_ean13.cpp
+++ b/xfa/fxbarcode/cbc_ean13.cpp
@@ -92,6 +92,10 @@
   return TRUE;
 }
 
+BC_TYPE CBC_EAN13::GetType() {
+  return BC_EAN13;
+}
+
 CFX_WideString CBC_EAN13::Decode(uint8_t* buf,
                                  int32_t width,
                                  int32_t height,