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

net/base/client_socket_handle.h

Index: net/base/client_socket_handle.h
diff --git a/net/base/client_socket_handle.h b/net/base/client_socket_handle.h
index e0d9e73175d3453c6f3a067529bb1bb56e53236c..1328369fcdaeb5bcae331b47c91a014a604322f0 100644
--- a/net/base/client_socket_handle.h
+++ b/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); }