Reland 54771 (and 54795) To enable TCP Preconnection by default...

chrome/browser/net/preconnect.cc

Index: chrome/browser/net/preconnect.cc
===================================================================
--- chrome/browser/net/preconnect.cc	(revision 55108)
+++ chrome/browser/net/preconnect.cc	(working copy)
@@ -21,18 +21,22 @@
 // static
 bool Preconnect::preconnect_despite_proxy_ = false;
 
-// We will deliberately leak this singular instance, which is used only for
-// callbacks.
-// static
-Preconnect* Preconnect::callback_instance_;
 
+Preconnect::~Preconnect() {
+  if (!handle_.is_initialized())
+    return;
+  DCHECK(motivation_ == UrlInfo::LEARNED_REFERAL_MOTIVATED ||
+         motivation_ == UrlInfo::OMNIBOX_MOTIVATED);
+  if (motivation_ == UrlInfo::OMNIBOX_MOTIVATED)
+    handle_.socket()->SetOmniboxSpeculation();
+  else
+    handle_.socket()->SetSubresourceSpeculation();
+  handle_.Reset();
+}
+
 // static
 void Preconnect::PreconnectOnUIThread(const GURL& url,
     UrlInfo::ResolutionMotivation motivation) {
-  // Try to do connection warming for this search provider.
-  URLRequestContextGetter* getter = Profile::GetDefaultRequestContext();
-  if (!getter)
-    return;
   // Prewarm connection to Search URL.
   ChromeThread::PostTask(
       ChromeThread::IO,
@@ -57,6 +61,13 @@
 // static
 void Preconnect::PreconnectOnIOThread(const GURL& url,
     UrlInfo::ResolutionMotivation motivation) {
+  scoped_refptr<Preconnect> preconnect = new Preconnect(motivation);
+  // TODO(jar): Should I use PostTask for LearnedSubresources to delay the
+  // preconnection a tad?
+  preconnect->Connect(url);
+}
+
+void Preconnect::Connect(const GURL& url) {
   URLRequestContextGetter* getter = Profile::GetDefaultRequestContext();
   if (!getter)
     return;
@@ -64,6 +75,9 @@
     LOG(DFATAL) << "This must be run only on the IO thread.";
     return;
   }
+
+  AddRef();  // Stay alive until socket is available.
+
   URLRequestContext* context = getter->GetURLRequestContext();
 
   if (preconnect_despite_proxy_) {
@@ -86,16 +100,12 @@
     }
   }
 
-  UMA_HISTOGRAM_ENUMERATION("Net.PreconnectMotivation", motivation,
+  UMA_HISTOGRAM_ENUMERATION("Net.PreconnectMotivation", motivation_,
                             UrlInfo::MAX_MOTIVATED);
 
   net::HttpTransactionFactory* factory = context->http_transaction_factory();
   net::HttpNetworkSession* session = factory->GetSession();
 
-  net::ClientSocketHandle handle;
-  if (!callback_instance_)
-    callback_instance_ = new Preconnect;
-
   scoped_refptr<net::TCPSocketParams> tcp_params =
       new net::TCPSocketParams(url.host(), url.EffectiveIntPort(), net::LOW,
                                GURL(), false);
@@ -103,6 +113,19 @@
   net::HostPortPair endpoint(url.host(), url.EffectiveIntPort());
   std::string group_name = endpoint.ToString();
 
+  // It almost doesn't matter whether we use net::LOWEST or net::HIGHEST
+  // priority here, as we won't make a request, and will surrender the created
+  // socket to the pool as soon as we can.  However, we would like to mark the
+  // speculative socket as such, and IF we use a net::LOWEST priority, and if
+  // a navigation asked for a socket (after us) then it would get our socket,
+  // and we'd get its later-arriving socket, which might make us record that
+  // the speculation didn't help :-/.  By using net::HIGHEST, we ensure that
+  // a socket is given to us if "we asked first" and this allows us to mark it
+  // as speculative, and better detect stats (if it gets used).
+  // TODO(jar): histogram to see how often we accidentally use a previously-
+  // unused socket, when a previously used socket was available.
+  net::RequestPriority priority = net::HIGHEST;
+
   if (url.SchemeIs("https")) {
     group_name = StringPrintf("ssl/%s", group_name.c_str());
 
@@ -120,21 +143,20 @@
     const scoped_refptr<net::SSLClientSocketPool>& pool =
         session->ssl_socket_pool();
 
-    handle.Init(group_name, ssl_params, net::LOWEST, callback_instance_, pool,
-                net::BoundNetLog());
-    handle.Reset();
+    handle_.Init(group_name, ssl_params, priority, this, pool,
+                 net::BoundNetLog());
     return;
   }
 
   const scoped_refptr<net::TCPClientSocketPool>& pool =
       session->tcp_socket_pool();
-  handle.Init(group_name, tcp_params, net::LOWEST, callback_instance_, pool,
-              net::BoundNetLog());
-  handle.Reset();
+  handle_.Init(group_name, tcp_params, priority, this, pool,
+               net::BoundNetLog());
 }
 
 void Preconnect::RunWithParams(const Tuple1<int>& params) {
-  // This will rarely be called, as we reset the connection just after creating.
-  NOTREACHED();
+  if (params.a < 0 && handle_.socket())
+    handle_.socket()->Disconnect();
+  Release();
 }
 }  // chrome_browser_net