This avoids integer overflows when size_t is 32 bits, and conforms
to style guide recommendations to avoid unsigned integers.
Also add tests for overflow on RateStatistics accumulator.
Bug: webrtc:11247
Change-Id: Ifa0db567f41bbcf3ec46d89ab888f2ed9d03f3f0
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/163991
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Yves Gerey <yvesg@google.com>
Cr-Commit-Position: refs/heads/master@{#30268}