Adaptively identify URL subresources and pre-resolve hosts via DNS

Use the HTTP "referer" header to identify subresources used during a
page load.  Store that info, and use it when next visiting the referenced
hosts to pre-resolve the (probably) needed subresources.

This set of changes will surely evolve as we see how it plays out
on broader distribution (via histogram measurments), but this should be
the foundation of the change.

In design specs, this was previously referred to as "adaptive correlated
DNS prefetching."

r=mbelshe


Review URL: http://codereview.chromium.org/9168

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@4929 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 15 insertions, 5 deletions

diff --git a/net/base/dns_resolution_observer.cc b/net/base/dns_resolution_observer.cc
index 46416d4..0b2e9d5 100644
--- a/net/base/dns_resolution_observer.cc
+++ b/net/base/dns_resolution_observer.cc
@@ -47,10 +47,13 @@ void DidStartDnsResolution(const std::string& name, void* context) {
     current_observer->OnStartResolution(name, context);
 }
 
-void DidFinishDnsResolutionWithStatus(bool was_resolved, void* context) {
+void DidFinishDnsResolutionWithStatus(bool was_resolved,
+                                      const GURL& referrer,
+                                      void* context) {
   DnsResolutionObserver* current_observer = dns_resolution_observer;
   if (current_observer) {
-    current_observer->OnFinishResolutionWithStatus(was_resolved, context);
+    current_observer->OnFinishResolutionWithStatus(was_resolved, referrer,
+                                                   context);
   }
 }
 
diff --git a/net/base/dns_resolution_observer.h b/net/base/dns_resolution_observer.h
index 1fd3c74..b03897d 100644
--- a/net/base/dns_resolution_observer.h
+++ b/net/base/dns_resolution_observer.h
@@ -15,6 +15,8 @@
 
 #include <string>
 
+#include "googleurl/src/gurl.h"
+
 namespace net {
 
 class DnsResolutionObserver {
@@ -30,8 +32,10 @@ class DnsResolutionObserver {
   // Once a matching pair of notifications has been provided (i.e., a pair with
   // identical context values), and the notification methods (below) have
   // returned, the context values *might* be reused.
-  virtual void OnStartResolution(const std::string& name, void* context) = 0;
+  virtual void OnStartResolution(const std::string& host_name,
+                                 void* context) = 0;
   virtual void OnFinishResolutionWithStatus(bool was_resolved,
+                                            const GURL& referrer,
                                             void* context) = 0;
 };
 
@@ -51,8 +55,11 @@ DnsResolutionObserver* RemoveDnsResolutionObserver();
 // The following functions are expected to be called only by network stack
 // implementations.  This above observer class will relay the notifications
 // to any registered observer.
-void DidStartDnsResolution(const std::string& name, void* context);
-void DidFinishDnsResolutionWithStatus(bool was_resolved, void* context);
+void DidStartDnsResolution(const std::string& name,
+                           void* context);
+void DidFinishDnsResolutionWithStatus(bool was_resolved,
+                                      const GURL& url,
+                                      void* context);
 }  // namspace net
 
 #endif  // NET_BASE_DNS_RESOLUTION_OBSERVER_H_