Persist info about subresources on pages for DNS pre-resolution

The DNS pre-resolution system already "learns" what domains are commonly
needed when rendering sub-resources of a page at a given domain.
This patch saves (some of) the information learned into a persistent
pref, and restores it on startup.

For now, I put in a wimpy pruning of the list each time I save, so that
the list will not grow endlessly from session to session.  I probably need
a better pruning algorithm, such as one that prunes after a given amount
of time, rather than only during shutdown.  For now, this should get
a lot of nice results, and provide slightly larger than needed lists to
users that have long lived sessions, which is similar to the current 
performance, where I didn't persist any info, and only pruned (actually
discarded) all learned info at shutdown.

r=mbelshe
Review URL: http://codereview.chromium.org/21374

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@9912 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 6 insertions, 0 deletions

diff --git a/chrome/browser/browser_shutdown.cc b/chrome/browser/browser_shutdown.cc
index d3d1b98..ef12384 100644
--- a/chrome/browser/browser_shutdown.cc
+++ b/chrome/browser/browser_shutdown.cc
@@ -114,6 +114,12 @@ void Shutdown() {
   PrefService* prefs = g_browser_process->local_state();
 
   chrome_browser_net::SaveHostNamesForNextStartup(prefs);
+  // TODO(jar): Trimming should be done more regularly, such as every 48 hours
+  // of physical time, or perhaps after 48 hours of running (excluding time
+  // between sessions possibly).
+  // For now, we'll just trim at shutdown.
+  chrome_browser_net::TrimSubresourceReferrers();
+  chrome_browser_net::SaveSubresourceReferrers(prefs);
 
   MetricsService* metrics = g_browser_process->metrics_service();
   if (metrics) {