Avoid doing concurrent DNS resolves of the same hostname

net/url_request/url_request_context.h

 // Copyright (c) 2006-2008 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.
 
 // This class represents contextual information (cookies, cache, etc.)
 // that's useful when processing resource requests.
 // The class is reference-counted so that it can be cleaned up after any
 // requests that are using it have been completed.
 
 #ifndef NET_URL_REQUEST_URL_REQUEST_CONTEXT_H_
 #define NET_URL_REQUEST_URL_REQUEST_CONTEXT_H_
 
 #include "base/ref_counted.h"
 #include "base/string_util.h"
 #include "net/base/cookie_policy.h"
 #include "net/ftp/ftp_auth_cache.h"
 
 namespace net {
 class CookieMonster;
 class ForceTLSState;
 class FtpTransactionFactory;
+class HostResolver;
 class HttpTransactionFactory;
 class ProxyService;
 }
 
 // Subclass to provide application-specific context for URLRequest instances.
 class URLRequestContext :
     public base::RefCountedThreadSafe<URLRequestContext> {
  public:
   URLRequestContext()
-      : proxy_service_(NULL),
+      : host_resolver_(NULL),
+        proxy_service_(NULL),
         http_transaction_factory_(NULL),
         ftp_transaction_factory_(NULL),
         cookie_store_(NULL),
         force_tls_state_(NULL) {
   }
 
+  net::HostResolver* host_resolver() const {
+    return host_resolver_;
+  }
+
   // Get the proxy service for this context.
   net::ProxyService* proxy_service() const {
     return proxy_service_;
   }
 
   // Gets the http transaction factory for this context.
   net::HttpTransactionFactory* http_transaction_factory() {
     return http_transaction_factory_;
   }
 
@@ skipping 33 matching lines @@
     referrer_charset_ = charset;
   }
 
  protected:
   friend class base::RefCountedThreadSafe<URLRequestContext>;
 
   virtual ~URLRequestContext() {}
 
   // The following members are expected to be initialized and owned by
   // subclasses.
+  net::HostResolver* host_resolver_;
   net::ProxyService* proxy_service_;
   net::HttpTransactionFactory* http_transaction_factory_;
   net::FtpTransactionFactory* ftp_transaction_factory_;
   net::CookieMonster* cookie_store_;
   net::CookiePolicy cookie_policy_;
   net::ForceTLSState* force_tls_state_;;
   net::FtpAuthCache ftp_auth_cache_;
   std::string accept_language_;
   std::string accept_charset_;
   // The charset of the referrer where this request comes from. It's not
   // used in communication with a server but is used to construct a suggested
   // filename for file download.
   std::string referrer_charset_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(URLRequestContext);
 };
 
 #endif  // NET_URL_REQUEST_URL_REQUEST_CONTEXT_H_