Add experiment on weak ping delay during call set up time

webrtc/p2p/base/p2ptransportchannel.h

Index: webrtc/p2p/base/p2ptransportchannel.h
diff --git a/webrtc/p2p/base/p2ptransportchannel.h b/webrtc/p2p/base/p2ptransportchannel.h
index 51979df8d8e1fe8a277368ea0684f36dbbb89d6b..e49fc2732381abdfd7e9d51f391633157d62f93d 100644
--- a/webrtc/p2p/base/p2ptransportchannel.h
+++ b/webrtc/p2p/base/p2ptransportchannel.h
@@ -34,6 +34,8 @@
 
 namespace cricket {
 
+extern const uint32_t WEAK_PING_DELAY;
+
 // Adds the port on which the candidate originated.
 class RemoteCandidate : public Candidate {
  public:
@@ -252,6 +254,7 @@ class P2PTransportChannel : public TransportChannelImpl,
   int receiving_timeout_;
   uint32_t last_ping_sent_ms_ = 0;
   bool gather_continually_ = false;
+  int weak_ping_delay_ = WEAK_PING_DELAY;
 
   RTC_DISALLOW_COPY_AND_ASSIGN(P2PTransportChannel);
 };