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

net/base/host_resolver.h

 // 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.
 
 #ifndef NET_BASE_HOST_RESOLVER_H_
 #define NET_BASE_HOST_RESOLVER_H_
 
 #include <string>
 
 #include "base/ref_counted.h"
@@ skipping 113 matching lines @@
 
     // Called when request |id| has been cancelled. A request is "cancelled"
     // if either the HostResolver is destroyed while a resolution is in
     // progress, or HostResolver::CancelRequest() is called.
     virtual void OnCancelResolution(int id, const RequestInfo& info) = 0;
   };
 
   // Opaque type used to cancel a request.
   typedef void* RequestHandle;
 
+  // This value can be passed into CreateSystemHostResolver as the
+  // |max_concurrent_resolves| parameter. It will select a default level of
+  // concurrency.
+  static const size_t kDefaultParallelism = 0;
+
   // Resolves the given hostname (or IP address literal), filling out the
   // |addresses| object upon success.  The |info.port| parameter will be set as
   // the sin(6)_port field of the sockaddr_in{6} struct.  Returns OK if
   // successful or an error code upon failure.
   //
   // When callback is null, the operation completes synchronously.
   //
   // When callback is non-null, the operation may be performed asynchronously.
   // If the operation cannnot be completed synchronously, ERR_IO_PENDING will
   // be returned and the real result code will be passed to the completion
@@ skipping 87 matching lines @@
 
   // Completion callback for when request to |resolver_| completes.
   net::CompletionCallbackImpl<SingleRequestHostResolver> callback_;
 
   DISALLOW_COPY_AND_ASSIGN(SingleRequestHostResolver);
 };
 
 // Creates a HostResolver implementation that queries the underlying system.
 // (Except if a unit-test has changed the global HostResolverProc using
 // ScopedHostResolverProc to intercept requests to the system).
-HostResolver* CreateSystemHostResolver();
+// |max_concurrent_resolves| is how many resolve requests will be allowed to
+// run in parallel. Pass HostResolver::kDefaultParallelism to choose a
+// default value.
+HostResolver* CreateSystemHostResolver(size_t max_concurrent_resolves);
 
 }  // namespace net
 
 #endif  // NET_BASE_HOST_RESOLVER_H_