Create a synthetic field trial for precache.

chrome/browser/precache/precache_manager_factory.cc

 // Copyright 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/precache/precache_manager_factory.h"
 
 #include <memory>
 #include <utility>
 
 #include "base/files/file_path.h"
 #include "chrome/browser/history/history_service_factory.h"
 #include "chrome/browser/net/spdyproxy/data_reduction_proxy_chrome_settings.h"
 #include "chrome/browser/net/spdyproxy/data_reduction_proxy_chrome_settings_factory.h"
+#include "chrome/browser/precache/precache_util.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/sync/profile_sync_service_factory.h"
 #include "components/keyed_service/content/browser_context_dependency_manager.h"
 #include "components/keyed_service/core/service_access_type.h"
 #include "components/precache/content/precache_manager.h"
 #include "components/precache/core/precache_database.h"
 #include "content/public/browser/browser_context.h"
 
 namespace precache {
 
@@ skipping 29 matching lines @@
       base::FilePath(FILE_PATH_LITERAL("PrecacheDatabase"))));
   return new PrecacheManager(
       browser_context,
       ProfileSyncServiceFactory::GetSyncServiceForBrowserContext(
           browser_context),
       HistoryServiceFactory::GetForProfile(
           Profile::FromBrowserContext(browser_context),
           ServiceAccessType::IMPLICIT_ACCESS),
       DataReductionProxyChromeSettingsFactory::GetForBrowserContext(
           browser_context),
-      db_path, std::move(precache_database));
+      db_path, std::move(precache_database),
+      base::Bind(&precache::RegisterPrecacheSyntheticFieldTrial));
 }
 
 }  // namespace precache