Use size_t for loop counter to avoid sign comparison warning
Use size_t for loop counter to avoid sign comparison warning

BUG= 462791
TEST= trybots

Review URL: https://codereview.chromium.org/1419373002

sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client