Add UMA metrics for ICE regathering reasons.

webrtc/p2p/client/basicportallocator.cc

Index: webrtc/p2p/client/basicportallocator.cc
diff --git a/webrtc/p2p/client/basicportallocator.cc b/webrtc/p2p/client/basicportallocator.cc
index dba68f177e5120a496a39d603d622971ac776ac4..8a3bbcea43b5d6b8f139ad94618e9f0253474d0d 100644
--- a/webrtc/p2p/client/basicportallocator.cc
+++ b/webrtc/p2p/client/basicportallocator.cc
@@ -14,6 +14,7 @@
 #include <string>
 #include <vector>
 
+#include "webrtc/api/peerconnectioninterface.h"
 #include "webrtc/p2p/base/basicpacketsocketfactory.h"
 #include "webrtc/p2p/base/common.h"
 #include "webrtc/p2p/base/port.h"
@@ -156,8 +157,11 @@ BasicPortAllocator::~BasicPortAllocator() {
 PortAllocatorSession* BasicPortAllocator::CreateSessionInternal(
     const std::string& content_name, int component,
     const std::string& ice_ufrag, const std::string& ice_pwd) {
-  return new BasicPortAllocatorSession(
+  PortAllocatorSession* session = new BasicPortAllocatorSession(
       this, content_name, component, ice_ufrag, ice_pwd);
+  session->SignalIceRegatheringReason.connect(
+      this, &BasicPortAllocator::OnIceRegatheringReason);
+  return session;
 }
 
 void BasicPortAllocator::AddTurnServer(const RelayServerConfig& turn_server) {
@@ -167,6 +171,15 @@ void BasicPortAllocator::AddTurnServer(const RelayServerConfig& turn_server) {
                    prune_turn_ports());
 }
 
+void BasicPortAllocator::OnIceRegatheringReason(PortAllocatorSession* session,
+                                                IceRegatheringReason reason) {
+  if (metrics_observer()) {
+    metrics_observer()->IncrementEnumCounter(
+        webrtc::kEnumCounterIceRegatheringReason, static_cast<int>(reason),
+        static_cast<int>(IceRegatheringReason::MAX_VALUE));

[Taylor Brandstetter, 2016/10/03 20:33:35]

Unless I'm mistaken, pooled BasicPortAllocatorSessions will increment the stat
even if they aren't used. Is that intended? It could skew the stats once pooling
becomes available in Chromium.

[honghaiz3, 2016/10/04 01:03:55]

It is true but only under the circumstances where you created sessions that were
not used and then network changed or failed. 
Should a session created in a pool being used right away or very soon?
After second thought, if a session was created in a pool and then a network
change happened and an ICE regathering happened, perhaps it should be counted
anyway because an ICE regathering indeed happened, even though it is not used. 
So it is probably intended. 

[Taylor Brandstetter, 2016/10/04 02:42:32]

If we do count regathering that occurs for pooled sessions, I think it needs to
increment a different stat than for in-use sessions. Because otherwise, we can't
answer a question like: "When regathering occurs for an active connection, how
often is it due to a network change vs. an ICE restart?"

[honghaiz3, 2016/10/05 05:01:53]

Do not count the regathering for pooled sessions for now.  We could add that
later. 

+  }
+}
+
 // BasicPortAllocatorSession
 BasicPortAllocatorSession::BasicPortAllocatorSession(
     BasicPortAllocator* allocator,
@@ -247,7 +260,7 @@ void BasicPortAllocatorSession::StartGettingPorts() {
 
   network_thread_->Post(RTC_FROM_HERE, this, MSG_CONFIG_START);
 
-  LOG(LS_INFO) << "Pruning turn ports "
+  LOG(LS_INFO) << "Start getting ports with prune_turn_ports "
                << (prune_turn_ports_ ? "enabled" : "disabled");
 }
 
@@ -296,12 +309,20 @@ std::vector<rtc::Network*> BasicPortAllocatorSession::GetFailedNetworks() {
 }
 
 void BasicPortAllocatorSession::RegatherOnFailedNetworks() {
+  // Do not regather if the allocations has not started, the network manager has
+  // not started, or the session has stopped.
+  if (!allocation_started_ || !network_manager_started_ || IsStopped()) {

[Taylor Brandstetter, 2016/10/03 20:33:35]

This seems separate to adding stats. Could you put it in a different CL, or make
sure this CL's description mentions it?

[honghaiz3, 2016/10/04 01:03:55]

Moved away from this CL. 

+    return;
+  }
+
   // Find the list of networks that have no connection.
   std::vector<rtc::Network*> failed_networks = GetFailedNetworks();
   if (failed_networks.empty()) {
     return;
   }
 
+  LOG(LS_INFO) << "Regather candidates on failed networks";
+
   // Mark a sequence as "network failed" if its network is in the list of failed
   // networks, so that it won't be considered as equivalent when the session
   // regathers ports and candidates.
@@ -321,9 +342,10 @@ void BasicPortAllocatorSession::RegatherOnFailedNetworks() {
     PrunePortsAndRemoveCandidates(ports_to_prune);
   }
 
-  if (allocation_started_ && network_manager_started_) {
-    DoAllocate();
-  }
+  SignalIceRegatheringReason(
+      this, IceRegatheringReason::CONTINUAL_GATHERING_BY_NETWORK_FAILURE);
+
+  DoAllocate();
 }
 
 std::vector<PortInterface*> BasicPortAllocatorSession::ReadyPorts() const {
@@ -501,7 +523,7 @@ void BasicPortAllocatorSession::AllocatePorts() {
 }
 
 void BasicPortAllocatorSession::OnAllocate() {
-  if (network_manager_started_)
+  if (network_manager_started_ && !IsStopped())

[Taylor Brandstetter, 2016/10/03 20:33:35]

Same here.

[honghaiz3, 2016/10/04 01:03:55]

This is not a behavior change. 
I just moved the check of IsStopped from the DoAllocate to the outside of the
call. 
I need this change in this CL because I do not want to signal an
ICERegatheringReason when the session has stopped. 

[Taylor Brandstetter, 2016/10/04 02:42:32]

Acknowledged.

[honghaiz3, 2016/10/05 05:01:53]

Acknowledged.

     DoAllocate();
 
   allocation_started_ = true;
@@ -553,10 +575,6 @@ std::vector<rtc::Network*> BasicPortAllocatorSession::GetNetworks() {
 void BasicPortAllocatorSession::DoAllocate() {
   bool done_signal_needed = false;
   std::vector<rtc::Network*> networks = GetNetworks();
-
-  if (IsStopped()) {
-    return;
-  }
   if (networks.empty()) {
     LOG(LS_WARNING) << "Machine has no networks; no ports will be allocated";
     done_signal_needed = true;
@@ -627,12 +645,19 @@ void BasicPortAllocatorSession::OnNetworksChanged() {
     PrunePortsAndRemoveCandidates(ports_to_prune);
   }
 
+  if (allocation_started_ && !IsStopped()) {
+    if (network_manager_started_) {
+      // If the network manager has started, it must be a regathering.
+      SignalIceRegatheringReason(
+          this, IceRegatheringReason::CONTINUAL_GATHERING_BY_NETWORK_CHANGE);
+    }
+    DoAllocate();
+  }
+
   if (!network_manager_started_) {
-    LOG(LS_INFO) << "Network manager is started";
+    LOG(LS_INFO) << "Network manager has started";
     network_manager_started_ = true;
   }
-  if (allocation_started_)
-    DoAllocate();
 }
 
 void BasicPortAllocatorSession::DisableEquivalentPhases(