Tell DNS prefetch when search URL is likely so that prewarming can be done...

chrome/browser/net/dns_global.cc

 // 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.
 
 #include "chrome/browser/net/dns_global.h"
 
 #include <map>
 #include <string>
 
 #include "base/singleton.h"
@@ skipping 99 matching lines @@
   } else {
     ChromeThread::PostTask(
         ChromeThread::IO,
         FROM_HERE,
         NewRunnableMethod(dns_master,
                           &DnsMaster::ResolveList, hostnames, motivation));
   }
 }
 
 // This API is used by the autocomplete popup box (where URLs are typed).
-void DnsPrefetchUrl(const GURL& url) {
+// It is only called on the UI thread.
+void DnsPrefetchUrl(const GURL& url, bool is_search_url) {
   DCHECK(ChromeThread::CurrentlyOn(ChromeThread::UI));
   if (!dns_prefetch_enabled || NULL == dns_master)
     return;
-  if (url.is_valid())
-    DnsMotivatedPrefetch(url.host(), DnsHostInfo::OMNIBOX_MOTIVATED);
+  if (!url.is_valid())
+    return;
+
+  static std::string last_host;
+  bool new_host = (url.host() != last_host);
+  if (new_host)
+    last_host = url.host();
+
+  // Omnibox tends to call in pairs (just a few milliseconds apart), and we
+  // really don't need to keep resolving a name that often.
+  static base::Time last_prefetch_for_host;
+  static base::Time last_tcp_warm_for_host;
+  base::Time now = base::Time::Now();
+  if (!new_host) {
+    const int kMinPreresolveSeconds(10);
+    if (kMinPreresolveSeconds > (now - last_prefetch_for_host).InSeconds())
+      return;
+  }
+  last_prefetch_for_host = now;
+  DnsMotivatedPrefetch(last_host, DnsHostInfo::OMNIBOX_MOTIVATED);
+
+  if (!is_search_url)
+    return;
+  static base::Time last_keepalive;
+  const int kMaxSearchKeepaliveSeconds(90);  // TODO(jar): Track vendors.
+  if (!new_host &&
+      (now - last_keepalive).InSeconds() < kMaxSearchKeepaliveSeconds)
+    return;
+  last_keepalive = now;
+  // Prewarm connection to Search URL.
 }
 
 static void DnsMotivatedPrefetch(const std::string& hostname,
                                  DnsHostInfo::ResolutionMotivation motivation) {
   DCHECK(ChromeThread::CurrentlyOn(ChromeThread::UI));
   if (!dns_prefetch_enabled || NULL == dns_master || !hostname.size())
     return;
 
   ChromeThread::PostTask(
       ChromeThread::IO,
@@ skipping 478 matching lines @@
     TimeDelta max_queueing_delay(
         TimeDelta::FromMilliseconds(max_queueing_delay_ms));
 
     DCHECK(!dns_master);
     InitDnsPrefetch(max_queueing_delay, max_concurrent, user_prefs,
                     local_state);
   }
 }
 
 }  // namespace chrome_browser_net