Added method for getting default module state and protect agains a

read/write race for child_modules_.

BUG=2731
TEST=tsan
R=stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/5919005

git-svn-id: http://webrtc.googlecode.com/svn/trunk@5306 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.h

@@ -418,6 +418,8 @@ class ModuleRtpRtcpImpl : public RtpRtcp {
   void set_rtt_ms(uint32_t rtt_ms);
   uint32_t rtt_ms() const;
 
+  bool IsDefaultModule() const;
+
   int32_t             id_;
   const bool                audio_;
   bool                      collision_detected_;