Make three simultanious prerenders the default maximum in Canary and Dev only.

chrome/browser/prerender/prerender_manager.cc

Index: chrome/browser/prerender/prerender_manager.cc
diff --git a/chrome/browser/prerender/prerender_manager.cc b/chrome/browser/prerender/prerender_manager.cc
index 6eee18a1182ec0649edf7d5c864de602fed8d9fc..5cdeccdcf82806e04abc277ede9785db19a274a8 100644
--- a/chrome/browser/prerender/prerender_manager.cc
+++ b/chrome/browser/prerender/prerender_manager.cc
@@ -69,9 +69,6 @@ const int kWindowDurationSeconds = 30;
 // Time interval at which periodic cleanups are performed.
 const int kPeriodicCleanupIntervalMs = 1000;
 
-// Time interval before a new prerender is allowed.
-const int kMinTimeBetweenPrerendersMs = 500;
-
 // Valid HTTP methods for prerendering.
 const char* const kValidHttpMethods[] = {
   "GET",
@@ -196,6 +193,10 @@ PrerenderManager::PrerenderManager(Profile* profile,
   // Any other checks simply make sure that the PrerenderManager is accessed on
   // the same thread that it was created on.
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+
+  if (GetMode() == PRERENDER_MODE_EXPERIMENT_ONE_PRERENDER_GROUP) {
+    config_.max_concurrency = 1;
+  }
 }
 
 PrerenderManager::~PrerenderManager() {
@@ -559,6 +560,8 @@ const char* PrerenderManager::GetModeString() {
       return "_5MinTTL";
     case PRERENDER_MODE_EXPERIMENT_NO_USE_GROUP:
       return "_NoUse";
+    case PRERENDER_MODE_EXPERIMENT_ONE_PRERENDER_GROUP:
+      return "_One";
     case PRERENDER_MODE_MAX:
       NOTREACHED() << "Invalid PrerenderManager mode.";
       break;
@@ -928,8 +931,6 @@ PrerenderHandle* PrerenderManager::AddPrerender(
   if (!prerender_contents || !prerender_contents->Init())
     return NULL;
 
-  histograms_->RecordPrerenderStarted(origin);
-
   // TODO(cbentzel): Move invalid checks here instead of PrerenderContents?
   active_prerender_list_.push_back(
       linked_ptr<PrerenderData>(new PrerenderData(this, prerender_contents)));
@@ -945,12 +946,14 @@ PrerenderHandle* PrerenderManager::AddPrerender(
                                         session_storage_namespace,
                                         control_group_behavior);
 
-  while (active_prerender_list_.size() > config_.max_elements) {
+  while (active_prerender_list_.size() > config_.max_concurrency) {
     prerender_contents = active_prerender_list_.front()->contents_;
     DCHECK(prerender_contents);
     prerender_contents->Destroy(FINAL_STATUS_EVICTED);
   }
 
+  histograms_->RecordPrerenderStarted(origin, active_prerender_list_.size());

[dominich, 2012/07/19 16:04:38]

changing this is bad - we'll have a mismatch between started and evicted which
Omnibox stats rely on.

Instead, record started as before and maybe separate the count tracking and do
that here.

[gavinp, 2012/07/23 18:35:21]

Done.

+
   StartSchedulingPeriodicCleanups();
   return prerender_handle;
 }