Migrate chrome/browser files to histogram_macros.h includes.

chrome/browser/extensions/external_pref_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/external_pref_loader.h"
 
 #include <utility>
 
 #include "base/bind.h"
 #include "base/files/file_enumerator.h"
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/json/json_file_value_serializer.h"
 #include "base/json/json_string_value_serializer.h"
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
-#include "base/metrics/histogram.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/path_service.h"
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "build/build_config.h"
 #include "chrome/browser/defaults.h"
 #include "chrome/browser/prefs/pref_service_syncable_util.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/sync/profile_sync_service_factory.h"
 #include "chrome/common/chrome_paths.h"
 #include "components/syncable_prefs/pref_service_syncable.h"
@@ skipping 302 matching lines @@
   LoadFinished();
 }
 
 ExternalTestingLoader::~ExternalTestingLoader() {}
 
 const base::FilePath ExternalTestingLoader::GetBaseCrxFilePath() {
   return fake_base_path_;
 }
 
 }  // namespace extensions