Refactor DNS A/B experient, and add test of congestion time limits

I added another option in the DNS experiment: user 2 seconds or 500ms
for the congestion limit (that causes pre-resolutions to be discarded
from the queue.

The code in browser_main.cc was getting toooo large, so I pulled all
the experiment code into dns_global.cc.

BUG=15479

r=eroman
Review URL: http://codereview.chromium.org/147215

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@19464 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 2 insertions, 47 deletions

diff --git a/chrome/browser/browser_main.cc b/chrome/browser/browser_main.cc
index df94b45..91bc5e4 100644
--- a/chrome/browser/browser_main.cc
+++ b/chrome/browser/browser_main.cc
@@ -635,53 +635,8 @@ int BrowserMain(const MainFunctionParams& parameters) {
   net::EnsureWinsockInit();
 #endif  // defined(OS_WIN)
 
-  // Set up a field trial to see what disabling DNS pre-resolution does to
-  // latency of network transactions.
-  FieldTrial::Probability kDIVISOR = 100;
-  FieldTrial::Probability k_PROBABILITY_PER_GROUP = 10;  // 10% probability.
-  // For options we don't (currently) wish to test, we use zero probability.
-  FieldTrial::Probability k_PROBABILITY_DISABLED = 0;
-  scoped_refptr<FieldTrial> dns_trial = new FieldTrial("DnsImpact", kDIVISOR);
-
-  // First option is to disable prefetching completele.
-  dns_trial->AppendGroup("_disabled_prefetch", k_PROBABILITY_PER_GROUP);
-  // Second option is to set parallel prefetch limit to 4 instead of default 8.
-  int parallel_4_prefetch = dns_trial->AppendGroup("_parallel_4_prefetch",
-                                                   k_PROBABILITY_PER_GROUP);
-
-  // Don't discard names (erase these lines) yet, as we may use them, and we
-  // have histogram data named for these options.
-
-  // Next two options relate to the number of parallel http connections that can
-  // be made to a single host.  The default is currently 6, and we wanted to see
-  // what would happen when we restricted this to 4.  (Historically the limit
-  // was a mere 2, but several browsers including Chromium increased it to 6
-  // recently).
-  int disabled_plus_4_connections = dns_trial->AppendGroup(
-      "_disabled_prefetch_4_connections", k_PROBABILITY_DISABLED);
-  int enabled_plus_4_connections = dns_trial->AppendGroup(
-      "_enabled_prefetch_4_connections", k_PROBABILITY_DISABLED);
-
-  scoped_ptr<chrome_browser_net::DnsPrefetcherInit> dns_prefetch_init;
-  if (dns_trial->group() == FieldTrial::kNotParticipating ||
-    dns_trial->group() == enabled_plus_4_connections ||
-    dns_trial->group() == parallel_4_prefetch) {
-    // Initialize the DNS prefetch system
-      if (dns_trial->group() == parallel_4_prefetch)
-        dns_prefetch_init.reset(new chrome_browser_net::DnsPrefetcherInit(
-            4, user_prefs));
-      else
-        dns_prefetch_init.reset(new chrome_browser_net::DnsPrefetcherInit(
-            chrome_browser_net::DnsPrefetcherInit::kMaxConcurrentLookups,
-            user_prefs));
-    chrome_browser_net::DnsPrefetchHostNamesAtStartup(user_prefs, local_state);
-    chrome_browser_net::RestoreSubresourceReferrers(local_state);
-  }
-
-  if (dns_trial->group() == disabled_plus_4_connections ||
-      dns_trial->group() == enabled_plus_4_connections) {
-    net::HttpNetworkSession::set_max_sockets_per_group(4);
-  }
+  // Initialize and maintain DNS prefetcher module.
+  chrome_browser_net::DnsPrefetcherInit dns_prefetch(user_prefs, local_state);
 
   scoped_refptr<FieldTrial> http_prioritization_trial =
       new FieldTrial("HttpPrioritization", 100);