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_code39.cpp b/xfa/fxbarcode/cbc_code39.cpp
index 03e618e..2b9852a 100644
--- a/xfa/fxbarcode/cbc_code39.cpp
+++ b/xfa/fxbarcode/cbc_code39.cpp
@@ -90,6 +90,10 @@
   return TRUE;
 }
 
+BC_TYPE CBC_Code39::GetType() {
+  return BC_CODE39;
+}
+
 CFX_WideString CBC_Code39::Decode(uint8_t* buf,
                                   int32_t width,
                                   int32_t height,