WebRTC 4521: Remove usage of deprecated timezone global variable

BUG=4521
R=pthatcher@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/56469004

Cr-Commit-Position: refs/heads/master@{#9285}

webrtc/base/httpcommon.cc

@@ -387,6 +387,10 @@ bool HttpDateToSeconds(const std::string& date, time_t* seconds) {
   tm *tm_for_timezone = localtime(&gmt);
   *seconds = gmt + tm_for_timezone->tm_gmtoff;
 #else
+#if _MSC_VER >= 1900
+  long timezone = 0;
+  _get_timezone(&timezone);
+#endif
   *seconds = gmt - timezone;
 #endif
   return true;