message: Return unavailable rate rather than garbage value.
  This CL quiets UBSan when value doesn't fit uint32_t.
  Cr-Commit-Position: refs/heads/master@{#30132}
diff: #include "rtc_base/rate_statistics.h"
  #include <algorithm>
  +#include <limits>
  #include <memory>
  #include "rtc_base/checks.h"
  @@ -91,7 +92,13 @@ absl::optional<uint32_t> RateStatistics::Rate(int64_t now_ms) const {
  }
  float scale = scale_ / active_window_size;
  - return static_cast<uint32_t>(accumulated_count_ * scale + 0.5f);
  + float result = accumulated_count_ * scale + 0.5f;
  +
  + // Better return unavailable rate than garbage value (undefined behavior).
  + if (result > std::numeric_limits<uint32_t>::max()) {
  + return absl::nullopt;
  + }
  + return static_cast<uint32_t>(result);
  }
  void RateStatistics::EraseOld(int64_t now_ms) {
  