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

chrome/browser/extensions/extension_service.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/extensions/extension_service.h"
 
 #include <algorithm>
 #include <iterator>
 #include <set>
 
@@ skipping 1390 matching lines @@
   // Calling UnloadAllExtensionsForTest here triggers a false-positive presubmit
   // warning about calling test code in production.
   UnloadAllExtensionsInternal();
   component_loader_->LoadAll();
   extensions::InstalledLoader(this).LoadAllExtensions();
   // Don't call SetReadyAndNotifyListeners() since tests call this multiple
   // times.
 }
 
 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() {
   if (updater_)
     updater_->Start();
 
   OnBlacklistUpdated();
 }
 
 void ExtensionService::AddExtension(const Extension* extension) {
@@ skipping 1103 matching lines @@
 }
 
 void ExtensionService::OnProfileDestructionStarted() {
   ExtensionIdSet ids_to_unload = registry_->enabled_extensions().GetIDs();
   for (ExtensionIdSet::iterator it = ids_to_unload.begin();
        it != ids_to_unload.end();
        ++it) {
     UnloadExtension(*it, UnloadedExtensionInfo::REASON_PROFILE_SHUTDOWN);
   }
 }