Add a histogram to measure the number of idle sockets when a TCP connection is established.

Review URL: http://codereview.chromium.org/99205

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@14955 0039d316-1c4b-4281-b951-d872f2087c98

net/base/client_socket_handle.h

@@ -62,6 +62,7 @@ class ClientSocketHandle {
   bool is_initialized() const { return socket_ != NULL; }
 
   // These may only be used if is_initialized() is true.
+  const std::string& group_name() const { return group_name_; }
   ClientSocket* socket() { return socket_->get(); }
   ClientSocket* release_socket() { return socket_->release(); }
   void set_socket(ClientSocket* s) { socket_->reset(s); }

net/base/client_socket_pool.cc

@@ -122,6 +122,14 @@ void ClientSocketPool::CloseIdleSockets() {
   CleanupIdleSockets(true);
 }
 
+int ClientSocketPool::IdleSocketCountInGroup(
+    const std::string& group_name) const {
+  GroupMap::const_iterator i = group_map_.find(group_name);
+  DCHECK(i != group_map_.end());
+
+  return i->second.idle_sockets.size();
+}
+
 bool ClientSocketPool::IdleSocket::ShouldCleanup(base::TimeTicks now) const {
   bool timed_out = (now - start_time) >=
       base::TimeDelta::FromSeconds(kIdleTimeout);

net/base/client_socket_pool.h

@@ -73,6 +73,9 @@ class ClientSocketPool : public base::RefCounted<ClientSocketPool> {
     return idle_socket_count_;
   }
 
+  // The total number of idle sockets in a connection group.
+  int IdleSocketCountInGroup(const std::string& group_name) const;
+
  private:
   friend class base::RefCounted<ClientSocketPool>;
 

net/http/http_network_transaction.cc

@@ -1033,6 +1033,12 @@ void HttpNetworkTransaction::LogTCPConnectedMetrics() const {
       host_resolution_and_tcp_connection_latency,
       base::TimeDelta::FromMilliseconds(1), base::TimeDelta::FromMinutes(10),
       100);
+
+  UMA_HISTOGRAM_COUNTS_100(
+      FieldTrial::MakeName(
+          "Net.TCP_Connection_Idle_Sockets", "DnsImpact").data(),
+      session_->connection_pool()->IdleSocketCountInGroup(
+          connection_.group_name()));
 }
 
 void HttpNetworkTransaction::LogTransactionConnectedMetrics() const {