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 df290e35c2fc677f1b34e26dcdb07809a2c3520d..6a214789172ebf5890295fc1216f57669d13ba5c 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/printing/print_dialog_cloud.h"
 #include "chrome/browser/process_singleton.h"
@@ -224,7 +225,7 @@ void BrowserMainParts::SetupFieldTrials() {
   ConnectionFieldTrial();
   SocketTimeoutFieldTrial();
   ProxyConnectionsFieldTrial();
-  PrefetchFieldTrial();
+  PrefetchAndPrerenderFieldTrial();
   SpdyFieldTrial();
   ConnectBackupJobsFieldTrial();
 }
@@ -429,7 +430,7 @@ void BrowserMainParts::SpdyFieldTrial() {
 // --disable-content-prefetch are set, use those to determine if
 // prefetch is enabled. Otherwise, randomly assign users to an A/B test for
 // prefetching.
-void BrowserMainParts::PrefetchFieldTrial() {
+void BrowserMainParts::PrefetchAndPrerenderFieldTrial() {
   if (parsed_command_line().HasSwitch(switches::kEnableContentPrefetch) ||
       parsed_command_line().HasSwitch(switches::kEnablePagePrerender))
     ResourceDispatcherHost::set_is_prefetch_enabled(true);
@@ -448,6 +449,16 @@ void BrowserMainParts::PrefetchFieldTrial() {
     ResourceDispatcherHost::set_is_prefetch_enabled(
         trial_grp == yes_prefetch_grp);
   }
+
+  PrerenderManager::PrerenderManagerMode prerender_mode;

[cbentzel, 2011/01/27 04:38:34]

Uninitialized values always scare me. Maybe change if/else to ternary, or
initialize to DISABLED. 

[gavinp, 2011/01/27 05:25:26]

Done.

+  if (parsed_command_line().HasSwitch(switches::kEnablePagePrerender))
+    prerender_mode = PrerenderManager::PRERENDER_MODE_ENABLED;
+  else
+    prerender_mode = PrerenderManager::PRERENDER_MODE_DISABLED;
+  PrerenderManager::SetMode(prerender_mode);
+
+  UMA_HISTOGRAM_ENUMERATION("Prerender.Sessions", prerender_mode,

[cbentzel, 2011/01/27 04:38:34]

Do we have other Prerender-prefixed histograms at this point, or is this the
first one?

[gavinp, 2011/01/27 05:25:26]

This is the first one.  I couldn't think of another group to put it in reviewing
them: ultimately I guess our histograms will be split between PLT and Prerender?

+                            PrerenderManager::PRERENDER_MODE_MAX);
 }
 
 // If neither --enable-connect-backup-jobs or --disable-connect-backup-jobs is