Add UMA for startup load time of component extensions. At the moment there is

chrome/browser/extensions/extension_service.cc

Index: chrome/browser/extensions/extension_service.cc
diff --git a/chrome/browser/extensions/extension_service.cc b/chrome/browser/extensions/extension_service.cc
index a93594708fc816d00a30ee1df19b28ffd2125a3f..f6801340b267e24550a386b180b4b44ce2ef480d 100644
--- a/chrome/browser/extensions/extension_service.cc
+++ b/chrome/browser/extensions/extension_service.cc
@@ -1408,11 +1408,14 @@ void ExtensionService::ReloadExtensionsForTest() {
 }
 
 void ExtensionService::SetReadyAndNotifyListeners() {
+  const base::TimeTicks start_time = base::TimeTicks::Now();
   ready_->Signal();
   content::NotificationService::current()->Notify(
       extensions::NOTIFICATION_EXTENSIONS_READY_DEPRECATED,
       content::Source<Profile>(profile_),
       content::NotificationService::NoDetails());
+  UMA_HISTOGRAM_TIMES("Extensions.ExtensionServiceNotifyReadyListenersTime",
+                      base::TimeTicks::Now() - start_time);
 }
 
 void ExtensionService::OnLoadedInstalledExtensions() {