[base] Use thread safe localtime_r() instead of localtime().

src/base/platform/platform-cygwin.cc

Index: src/base/platform/platform-cygwin.cc
diff --git a/src/base/platform/platform-cygwin.cc b/src/base/platform/platform-cygwin.cc
index a49e28723d21824d15b994a9ec5ade21f0da6e91..ba0f45667f333ce6df54d5b9dcaa63d0b1ac5fb3 100644
--- a/src/base/platform/platform-cygwin.cc
+++ b/src/base/platform/platform-cygwin.cc
@@ -29,7 +29,8 @@ namespace base {
 const char* OS::LocalTimezone(double time, TimezoneCache* cache) {
   if (std::isnan(time)) return "";
   time_t tv = static_cast<time_t>(std::floor(time/msPerSecond));
-  struct tm* t = localtime(&tv);  // NOLINT(runtime/threadsafe_fn)
+  struct tm tm;
+  struct tm* t = localtime_r(&tv, &tm);
   if (NULL == t) return "";
   return tzname[0];  // The location of the timezone string on Cygwin.
 }
@@ -39,7 +40,8 @@ double OS::LocalTimeOffset(TimezoneCache* cache) {
   // On Cygwin, struct tm does not contain a tm_gmtoff field.
   time_t utc = time(NULL);
   DCHECK(utc != -1);
-  struct tm* loc = localtime(&utc);  // NOLINT(runtime/threadsafe_fn)
+  struct tm tm;
+  struct tm* loc = localtime_r(&utc, &tm);
   DCHECK(loc != NULL);
   // time - localtime includes any daylight savings offset, so subtract it.
   return static_cast<double>((mktime(loc) - utc) * msPerSecond -