Delete the ClientSocketPoolHistograms class.

net/http/http_proxy_client_socket_pool.h

Index: net/http/http_proxy_client_socket_pool.h
diff --git a/net/http/http_proxy_client_socket_pool.h b/net/http/http_proxy_client_socket_pool.h
index f9cee7ed3f49ed6453cdf6fc1958856ca9ab5039..824b15f5becab9d3a049533804b3987c08811968 100644
--- a/net/http/http_proxy_client_socket_pool.h
+++ b/net/http/http_proxy_client_socket_pool.h
@@ -19,7 +19,6 @@
 #include "net/http/proxy_client_socket.h"
 #include "net/socket/client_socket_pool.h"
 #include "net/socket/client_socket_pool_base.h"
-#include "net/socket/client_socket_pool_histograms.h"
 #include "net/socket/ssl_client_socket.h"
 #include "net/spdy/spdy_session.h"
 
@@ -188,7 +187,6 @@ class NET_EXPORT_PRIVATE HttpProxyClientSocketPool
 
   HttpProxyClientSocketPool(int max_sockets,
                             int max_sockets_per_group,
-                            ClientSocketPoolHistograms* histograms,
                             TransportClientSocketPool* transport_pool,
                             SSLClientSocketPool* ssl_pool,
                             NetLog* net_log);
@@ -233,8 +231,6 @@ class NET_EXPORT_PRIVATE HttpProxyClientSocketPool
 
   base::TimeDelta ConnectionTimeout() const override;
 
-  ClientSocketPoolHistograms* histograms() const override;
-
   // LowerLayeredPool implementation.
   bool IsStalled() const override;