Avoid doing concurrent DNS resolves of the same hostname

net/url_request/url_request_context.h

Index: net/url_request/url_request_context.h
===================================================================
--- net/url_request/url_request_context.h	(revision 18213)
+++ net/url_request/url_request_context.h	(working copy)
@@ -19,6 +19,7 @@
 class CookieMonster;
 class ForceTLSState;
 class FtpTransactionFactory;
+class HostResolver;
 class HttpTransactionFactory;
 class ProxyService;
 }
@@ -28,13 +29,18 @@
     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_;
@@ -88,6 +94,7 @@
 
   // 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_;