Refactor Extension initialization logic. Add tracing and additional histogram.

extensions/browser/process_manager.cc

Index: extensions/browser/process_manager.cc
diff --git a/extensions/browser/process_manager.cc b/extensions/browser/process_manager.cc
index 10cce73440d463ce220ef6b7221c0f0cc9a6e143..5b0bdc4e60792a6279e6a384f1666ce2df8b9da3 100644
--- a/extensions/browser/process_manager.cc
+++ b/extensions/browser/process_manager.cc
@@ -753,14 +753,13 @@ void ProcessManager::SetEventPageSuspendingTimeForTesting(
 void ProcessManager::Observe(int type,
                              const content::NotificationSource& source,
                              const content::NotificationDetails& details) {
+  TRACE_EVENT0("browser,startup", "ProcessManager::Observe");
   switch (type) {
     case extensions::NOTIFICATION_EXTENSIONS_READY_DEPRECATED: {
       // TODO(jamescook): Convert this to use ExtensionSystem::ready() instead
       // of a notification.
-      const base::TimeTicks start_time = base::TimeTicks::Now();
+      SCOPED_UMA_HISTOGRAM_TIMER("Extensions.ProcessManagerStartupHostsTime");
       MaybeCreateStartupBackgroundHosts();
-      UMA_HISTOGRAM_TIMES("Extensions.ProcessManagerStartupHostsTime",
-                          base::TimeTicks::Now() - start_time);
       break;
     }