Add Startup.BrowserView.FirstPaint / .CompositingEnded histograms.

chrome/browser/background/background_mode_manager.cc

Index: chrome/browser/background/background_mode_manager.cc
diff --git a/chrome/browser/background/background_mode_manager.cc b/chrome/browser/background/background_mode_manager.cc
index 56524fb60a19144150520ce95f584c55c3c07e20..096064f033b1e7905c595ed9e4cfb814a4b1e538 100644
--- a/chrome/browser/background/background_mode_manager.cc
+++ b/chrome/browser/background/background_mode_manager.cc
@@ -57,6 +57,7 @@
 #include "chrome/grit/generated_resources.h"
 #include "components/prefs/pref_registry_simple.h"
 #include "components/prefs/pref_service.h"
+#include "components/startup_metric_utils/browser/startup_metric_utils.h"
 #include "content/public/browser/notification_service.h"
 #include "extensions/browser/extension_system.h"
 #include "extensions/common/constants.h"
@@ -717,6 +718,8 @@ void BackgroundModeManager::StartBackgroundMode() {
   if (in_background_mode_)
     return;
 
+  startup_metric_utils::SetBackgroundModeEnabled();
+
   // Mark ourselves as running in background mode.
   in_background_mode_ = true;