Pass expose-gc flag to pdfium test programs.
Pass expose-gc flag to pdfium test programs.

I also made the call to set the flags occur before the Initialize()
call, as this appears to be the pattern elsewhere in our codebase.

Review-Url: https://codereview.chromium.org/2627563003

DrAlexx/pdfium,DrAlexx/pdfium,DrAlexx/pdfium,DrAlexx/pdfium