Fix win unit tests broken at 9778206.
Fix win unit tests broken at 9778206.

Windows uses the system implementation of itoa which goes
to 36.

TBR=thestig@chromium.org

Review URL: https://codereview.chromium.org/1285433002 .

DrAlexx/pdfium,azunite/libpdfium,azunite/libpdfium,was4444/pdfium,azunite/libpdfium,DrAlexx/pdfium,azunite/libpdfium,andoma/pdfium,was4444/pdfium,andoma/pdfium,was4444/pdfium,andoma/pdfium,DrAlexx/pdfium,was4444/pdfium,DrAlexx/pdfium,andoma/pdfium