Fix format specifier for printing size_t.
Fix format specifier for printing size_t.

jdarpinian/web-ui-skeleton,google/latency-benchmark,jdarpinian/web-ui-skeleton,google/latency-benchmark,google/latency-benchmark,google/latency-benchmark,jdarpinian/web-ui-skeleton,jdarpinian/web-ui-skeleton,jdarpinian/web-ui-skeleton,google/latency-benchmark,google/latency-benchmark