Improve performance of proxy resolver by tracing DNS dependencies.

net/proxy/proxy_service_v8.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NET_PROXY_PROXY_SERVICE_V8_H_
 #define NET_PROXY_PROXY_SERVICE_V8_H_
 
 #include "base/basictypes.h"
 #include "net/base/net_export.h"
 
 namespace net {
 
 class DhcpProxyScriptFetcher;
 class HostResolver;
 class NetLog;
 class NetworkDelegate;
 class ProxyConfigService;
 class ProxyScriptFetcher;
 class ProxyService;
 
 // Creates a proxy service that polls |proxy_config_service| to notice when
 // the proxy settings change. We take ownership of |proxy_config_service|.
 //
-// |num_pac_threads| specifies the maximum number of threads to use for
-// executing PAC scripts. Threads are created lazily on demand.
-// If |0| is specified, then a default number of threads will be selected.
-//
-// Having more threads avoids stalling proxy resolve requests when the
-// PAC script takes a while to run. This is particularly a problem when PAC
-// scripts do synchronous DNS resolutions, since that can take on the order
-// of seconds.
-//
-// However, the disadvantages of using more than 1 thread are:
-//   (a) can cause compatibility issues for scripts that rely on side effects
-//       between runs (such scripts should not be common though).
-//   (b) increases the memory used by proxy resolving, as each thread will
-//       duplicate its own script context.
-
 // |proxy_script_fetcher| specifies the dependency to use for downloading
 // any PAC scripts. The resulting ProxyService will take ownership of it.
 //
 // |dhcp_proxy_script_fetcher| specifies the dependency to use for attempting
 // to retrieve the most appropriate PAC script configured in DHCP. The
 // resulting ProxyService will take ownership of it.
 //
 // |host_resolver| points to the host resolving dependency the PAC script
 // should use for any DNS queries. It must remain valid throughout the
 // lifetime of the ProxyService.
 //
 // ##########################################################################
 // # See the warnings in net/proxy/proxy_resolver_v8.h describing the
 // # multi-threading model. In order for this to be safe to use, *ALL* the
 // # other V8's running in the process must use v8::Locker.
 // ##########################################################################
 NET_EXPORT ProxyService* CreateProxyServiceUsingV8ProxyResolver(
     ProxyConfigService* proxy_config_service,
-    size_t num_pac_threads,
     ProxyScriptFetcher* proxy_script_fetcher,
     DhcpProxyScriptFetcher* dhcp_proxy_script_fetcher,
     HostResolver* host_resolver,
     NetLog* net_log,
     NetworkDelegate* network_delegate);
 
 }  // namespace net
 
 #endif  // NET_PROXY_PROXY_SERVICE_V8_H_