[presubmit] Enable runtime/threadsafe_fn linter checking.

src/base/platform/platform-macos.cc

Index: src/base/platform/platform-macos.cc
diff --git a/src/base/platform/platform-macos.cc b/src/base/platform/platform-macos.cc
index 4b760c3b863c50cb5b4a42ead6b0fc1fc25be80e..f16f329fc35e33feeb114f7eb175c2465b768e55 100644
--- a/src/base/platform/platform-macos.cc
+++ b/src/base/platform/platform-macos.cc
@@ -102,7 +102,7 @@ void OS::SignalCodeMovingGC() {
 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);
+  struct tm* t = localtime(&tv);  // NOLINT(runtime/threadsafe_fn)
   if (NULL == t) return "";
   return t->tm_zone;
 }
@@ -110,7 +110,7 @@ const char* OS::LocalTimezone(double time, TimezoneCache* cache) {
 
 double OS::LocalTimeOffset(TimezoneCache* cache) {
   time_t tv = time(NULL);
-  struct tm* t = localtime(&tv);
+  struct tm* t = localtime(&tv);  // NOLINT(runtime/threadsafe_fn)
   // tm_gmtoff includes any daylight savings offset, so subtract it.
   return static_cast<double>(t->tm_gmtoff * msPerSecond -
                              (t->tm_isdst > 0 ? 3600 * msPerSecond : 0));