run_javascript_tests.py: Be more flexible about directory layout.
run_javascript_tests.py: Be more flexible about directory layout.

The top-level directory name isn't part of the repository, and we
can't count on it always being "pdfium" (though many people will
choose to do it this way).

R=jam@chromium.org

Review URL: https://codereview.chromium.org/921043005

andoma/pdfium,azunite/pdf_clone,DrAlexx/pdfium,DrAlexx/pdfium,ttyangf/PDFium-,ttyangf/PDFium-,DrAlexx/pdfium,pwaller/pdfium,wwxxyx/pdfium0,azunite/pdfium_ch,was4444/pdfium,was4444/pdfium,csharpengineer/pdfium-code,klokantech/pdfium,nathanstitt/pdfium,was4444/pdfium,azunite/pdfium_ch,chenjian-rits/HelloWorld,azunite/libpdfium,duanhjlt/pdfium,nathanstitt/pdfium,duanhjlt/pdfium,chenjian-rits/HelloWorld,pwaller/pdfium,nathanstitt/pdfium,bradh/pdfium,wwxxyx/pdfium0,andoma/pdfium,azunite/pdf_clone,chenjian-rits/HelloWorld,klokantech/pdfium,ttyangf/PDFium-,azunite/libpdfium,rouault/pdfium,azunite/libpdfium,azunite/pdf_clone,wwxxyx/pdfium0,azunite/pdfium_ch,DrAlexx/pdfium,pwaller/pdfium,andoma/pdfium,csharpengineer/pdfium-code,andoma/pdfium,csharpengineer/pdfium-code,bradh/pdfium,duanhjlt/pdfium,duanhjlt/pdfium,was4444/pdfium,azunite/libpdfium,bradh/pdfium,klokantech/pdfium,rouault/pdfium,rouault/pdfium