Implement a 15 connection per proxy server limit.

net/proxy/proxy_server.h

Index: net/proxy/proxy_server.h
diff --git a/net/proxy/proxy_server.h b/net/proxy/proxy_server.h
index d07939618420a9f22d2b9c0dd070b50c1dc8ac4c..d7a94f0383602eccf8acb7eec63d9a5e9b13fd31 100644
--- a/net/proxy/proxy_server.h
+++ b/net/proxy/proxy_server.h
@@ -12,6 +12,7 @@
 #endif
 
 #include <string>
+#include "net/base/host_port_pair.h"
 
 namespace net {
 
@@ -65,8 +66,13 @@ class ProxyServer {
   int port() const;
 
   // Returns the <host>":"<port> string for the proxy server.
+  // TODO(willchan): Remove in favor of host_port_pair().
   std::string host_and_port() const;
 
+  // TODO(willchan): Change to const HostPortPair& after refactoring |host_| and
+  // |port_| here.
+  HostPortPair host_port_pair() const;
+
   // Parse from an input with format:
   //   [<scheme>"://"]<server>[":"<port>]
   //