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

chrome/browser/extensions/component_loader.cc

 // Copyright (c) 2012 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/component_loader.h"
 
 #include <string>
 
 #include "base/command_line.h"
 #include "base/files/file_util.h"
 #include "base/json/json_string_value_serializer.h"
 #include "base/metrics/field_trial.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/path_service.h"
+#include "base/time/time.h"
 #include "chrome/browser/extensions/extension_service.h"
 #include "chrome/browser/search/hotword_service.h"
 #include "chrome/browser/search/hotword_service_factory.h"
 #include "chrome/common/chrome_paths.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/chrome_version_info.h"
 #include "chrome/common/extensions/extension_constants.h"
 #include "chrome/grit/generated_resources.h"
 #include "components/crx_file/id_util.h"
 #include "content/public/browser/browser_context.h"
@@ skipping 93 matching lines @@
       local_state_(local_state),
       browser_context_(browser_context),
       extension_service_(extension_service),
       weak_factory_(this) {}
 
 ComponentLoader::~ComponentLoader() {
   ClearAllRegistered();
 }
 
 void ComponentLoader::LoadAll() {
+  base::TimeTicks start_time = base::TimeTicks::Now();

[Mark P, 2015/01/28 21:30:12]

nit: might as well be const

   for (RegisteredComponentExtensions::iterator it =
           component_extensions_.begin();
       it != component_extensions_.end(); ++it) {
     Load(*it);
   }
+  UMA_HISTOGRAM_TIMES("Extensions.LoadAllComponentTime",
+                      base::TimeTicks::Now() - start_time);
 }
 
 base::DictionaryValue* ComponentLoader::ParseManifest(
     const std::string& manifest_contents) const {
   JSONStringValueSerializer serializer(manifest_contents);
   scoped_ptr<base::Value> manifest(serializer.Deserialize(NULL, NULL));
 
   if (!manifest.get() || !manifest->IsType(base::Value::TYPE_DICTIONARY)) {
     LOG(ERROR) << "Failed to parse extension manifest.";
     return NULL;
@@ skipping 518 matching lines @@
         off_the_record_context, Extension::GetBaseURLFromExtensionId(id));
     storage::FileSystemContext* file_system_context =
         content::BrowserContext::GetStoragePartitionForSite(
             off_the_record_context, site)->GetFileSystemContext();
     file_system_context->EnableTemporaryFileSystemInIncognito();
   }
 #endif
 }
 
 }  // namespace extensions