Add experiment on weak ping delay during call set up time

webrtc/p2p/base/p2ptransportchannel.cc

Index: webrtc/p2p/base/p2ptransportchannel.cc
diff --git a/webrtc/p2p/base/p2ptransportchannel.cc b/webrtc/p2p/base/p2ptransportchannel.cc
index fc721312331233ad7db90f42164913fd5606bbb3..5a26d7c6c95bb5e40efa8e45892a2be629a56037 100644
--- a/webrtc/p2p/base/p2ptransportchannel.cc
+++ b/webrtc/p2p/base/p2ptransportchannel.cc
@@ -19,6 +19,7 @@
 #include "webrtc/base/crc32.h"
 #include "webrtc/base/logging.h"
 #include "webrtc/base/stringencode.h"
+#include "webrtc/system_wrappers/interface/field_trial.h"
 
 namespace {
 
@@ -220,7 +221,12 @@ P2PTransportChannel::P2PTransportChannel(const std::string& transport_name,
       remote_candidate_generation_(0),
       gathering_state_(kIceGatheringNew),
       check_receiving_delay_(MIN_CHECK_RECEIVING_DELAY * 5),
-      receiving_timeout_(MIN_CHECK_RECEIVING_DELAY * 50) {}
+      receiving_timeout_(MIN_CHECK_RECEIVING_DELAY * 50) {
+  uint32_t weak_ping_delay = ::strtoul(
+      webrtc::field_trial::FindFullName("WebRTC-WeakPingDelay").c_str(),

[pthatcher1, 2015/10/16 21:30:31]

While we call it "weak ping delay" internally, the name is a bit ugly.  I think
we may want a nicer one for the trial name.  How about
"WebRTC-StunInterPacketDelay"?

+      nullptr, 10);
+  weak_ping_delay_ = weak_ping_delay ? weak_ping_delay : WEAK_PING_DELAY;

[pthatcher1, 2015/10/16 21:30:31]

I think this would be more readable as:

if (weak_ping_delay) {
  weak_ping_delay_ = weak_ping_delay;
}

+}
 
 P2PTransportChannel::~P2PTransportChannel() {
   ASSERT(worker_thread_ == rtc::Thread::Current());
@@ -1156,7 +1162,7 @@ void P2PTransportChannel::OnCheckAndPing() {
   UpdateConnectionStates();
   // When the best connection is either not receiving or not writable,
   // switch to weak ping delay.
-  int ping_delay = weak() ? WEAK_PING_DELAY : STRONG_PING_DELAY;
+  int ping_delay = weak() ? weak_ping_delay_ : STRONG_PING_DELAY;
   if (rtc::Time() >= last_ping_sent_ms_ + ping_delay) {
     Connection* conn = FindNextPingableConnection();
     if (conn) {