Add histogram to track prerender sessions

chrome/browser/browser_main.cc

Index: chrome/browser/browser_main.cc
diff --git a/chrome/browser/browser_main.cc b/chrome/browser/browser_main.cc
index 38e9d337971a565056a5dcc3ee3f5f28a554ff1c..ad91bdf7e0ae65b0208951b35cb719d49dce2cca 100644
--- a/chrome/browser/browser_main.cc
+++ b/chrome/browser/browser_main.cc
@@ -56,6 +56,7 @@
 #include "chrome/browser/prefs/browser_prefs.h"
 #include "chrome/browser/prefs/pref_service.h"
 #include "chrome/browser/prefs/pref_value_store.h"
+#include "chrome/browser/prerender/prerender_manager.h"
 #include "chrome/browser/printing/cloud_print/cloud_print_proxy_service.h"
 #include "chrome/browser/process_singleton.h"
 #include "chrome/browser/profiles/profile.h"
@@ -1581,6 +1582,10 @@ int BrowserMain(const MainFunctionParams& parameters) {
   RecordBreakpadStatusUMA(metrics);
   about_flags::RecordUMAStatistics(user_prefs);
 
+  UMA_HISTOGRAM_ENUMERATION(

[cbentzel, 2011/01/26 16:55:46]

I'd really like this to be placed in PrefetchFieldTrial now so flag reading
happens in one centralized place, rather than both in PrefetchFieldTrial and
GetSessionType

[gavinp, 2011/01/27 04:29:29]

Done.

+      "Prerender.Sessions", PrerenderManager::GetSessionType(),
+      PrerenderManager::PRERENDERING_SESSION_TYPE_MAX);
+
   // Stat the directory with the inspector's files so that we can know if we
   // should display the entry in the context menu or not.
   browser_process->CheckForInspectorFiles();