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/common/pref_names.cc b/chrome/common/pref_names.cc
index 8c8dc76..b10f4f0 100644
--- a/chrome/common/pref_names.cc
+++ b/chrome/common/pref_names.cc
@@ -188,6 +188,12 @@ const wchar_t kDnsPrefetchingEnabled[] = L"dns_prefetching.enabled";
 // next startup, based on what was actually needed during this startup.
 const wchar_t kDnsStartupPrefetchList[] = L"StartupDNSPrefetchList";
 
+// A list of host names used to fetch web pages, and their commonly used
+// sub-resource hostnames (and expected latency benefits from pre-resolving such
+// sub-resource hostnames).
+// This list is adaptively grown and pruned.
+extern const wchar_t kDnsHostReferralList[] = L"HostReferralList";
+
 // The disabled messages in IPC logging.
 const wchar_t kIpcDisabledMessages[] = L"ipc_log_disabled_messages";