Conf. c++ coding guide (https://chromium.googlesource.com/chromium/src/+/master/styleguide/c++/c++.md#Types),
we may use size_t for vector indices, etc.

Bug: 
Change-Id: I578fb4199c061b006d03e1cc68e745868b40c227
Reviewed-on: https://chromium-review.googlesource.com/503590
Commit-Queue: Mircea Trofin <mtrofin@chromium.org>
Reviewed-by: Brad Nelson <bradnelson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45267}