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

chrome/browser/net/dns_global.cc

Index: chrome/browser/net/dns_global.cc
===================================================================
--- chrome/browser/net/dns_global.cc	(revision 43988)
+++ chrome/browser/net/dns_global.cc	(working copy)
@@ -117,12 +117,41 @@
 }
 
 // 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,