logging: use static stream in LogToFileRotate (#718)

We initialized the stream to write to in LogToFileRotate() but
it got deinitialized on the exit from the scope while its
reference remained in the logging which causes a crash on the
first write. That's a quick fix. More appropriately would be
to change webrtc function prototype for it to accept stream
for the ref count increment.

Signed-off-by: Dmitry Rogozhkin <dmitry.v.rogozhkin@intel.com>

Author: dvrogozh

talk/owt/sdk/base/logging.cc

@@ -37,7 +37,7 @@ void Logging::LogToConsole(LoggingSeverity severity) {
 }
 void Logging::LogToFileRotate(LoggingSeverity severity, std::string& dir, size_t max_log_size) {
   min_severity_ = severity;
-  std::shared_ptr<rtc::CallSessionFileRotatingLogSink> log_sink =
+  static std::shared_ptr<rtc::CallSessionFileRotatingLogSink> log_sink =
       std::make_shared<rtc::CallSessionFileRotatingLogSink>(dir, max_log_size);
   log_sink->Init();
   rtc::LogMessage::AddLogToStream(log_sink.get(), logging_severity_map[static_cast<int>(severity)]);