Convert ARRAYSIZE_UNSAFE -> arraysize in base/.

R=thestig@chromium.org
BUG=423134

Review URL: https://codereview.chromium.org/656033009

Cr-Commit-Position: refs/heads/master@{#299835}
StackTrace::StackTrace() {

#if !defined(__UCLIBC__)
  count_ = base::saturated_cast<size_t>(backtrace(trace_, arraysize(trace_)));
#else
  count_ = 0;
#endif
}

StackTrace::StackTrace() {

#if !defined(__UCLIBC__)
  count_ = base::saturated_cast<size_t>(backtrace(trace_, arraysize(trace_)));
#else
  count_ = 0;
#endif
}
