Fix windows compile: fix size_t vs. int mismatch

As indicated by:
http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_x64_rel_ng/builds/63417/steps/compile%20%28with%20patch%29/logs/stdio

R=thestig@chromium.org
TBR=thestig@chromium.org

Review URL: https://codereview.chromium.org/1160293003
1 file changed