Add a command line flag to change the default number of parallel DNS requests...

net/base/host_resolver_impl.cc

 // Copyright (c) 2010 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.
 
 #include "net/base/host_resolver_impl.h"
 
 #if defined(OS_WIN)
 #include <Winsock2.h>
 #elif defined(OS_POSIX)
 #include <netdb.h>
@@ skipping 34 matching lines @@
   HostCache* cache = new HostCache(
       kMaxHostCacheEntries,
       base::TimeDelta::FromMinutes(1),
       base::TimeDelta::FromSeconds(0));  // Disable caching of failed DNS.
 
   return cache;
 }
 
 }  // anonymous namespace
 
-HostResolver* CreateSystemHostResolver() {
+HostResolver* CreateSystemHostResolver(size_t max_concurrent_resolves) {
   // Maximum of 50 concurrent threads.
   // TODO(eroman): Adjust this, do some A/B experiments.
-  static const size_t kMaxJobs = 50u;
+  static const size_t kDefaultMaxJobs = 50u;
+
+  if (max_concurrent_resolves == HostResolver::kDefaultParallelism)
+    max_concurrent_resolves = kDefaultMaxJobs;
 
   HostResolverImpl* resolver =
-      new HostResolverImpl(NULL, CreateDefaultCache(), kMaxJobs);
+      new HostResolverImpl(NULL, CreateDefaultCache(),
+                           max_concurrent_resolves);
 
   return resolver;
 }
 
 static int ResolveAddrInfo(HostResolverProc* resolver_proc,
                            const std::string& host,
                            AddressFamily address_family,
                            HostResolverFlags host_resolver_flags,
                            AddressList* out,
                            int* os_error) {
@@ skipping 1077 matching lines @@
     if (r == req)
       return error;
 
     r->OnComplete(error, AddressList());
   }
 
   return ERR_IO_PENDING;
 }
 
 }  // namespace net