Implement a 15 connection per proxy server limit.

net/proxy/proxy_server.cc

Index: net/proxy/proxy_server.cc
diff --git a/net/proxy/proxy_server.cc b/net/proxy/proxy_server.cc
index 6c47feee06e02c3a58f5f3006eacf227c9e1b091..49038801d662a5283ad138a428d460233c595aa9 100644
--- a/net/proxy/proxy_server.cc
+++ b/net/proxy/proxy_server.cc
@@ -84,6 +84,13 @@ std::string ProxyServer::host_and_port() const {
   return host_ + ":" + IntToString(port_);
 }
 
+HostPortPair ProxyServer::host_port_pair() const {
+  // Doesn't make sense to call this if the URI scheme doesn't
+  // have concept of a host.
+  DCHECK(is_valid() && !is_direct());
+  return HostPortPair(host_, port_);
+}
+
 // static
 ProxyServer ProxyServer::FromURI(const std::string& uri,
                                  Scheme default_scheme) {