Make prefetch default on (subject to the regular predictive networking preference).

chrome/browser/prefetch/prefetch.cc

 // Copyright 2014 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/prefetch/prefetch.h"
 
 #include <string>
 
 #include "base/metrics/field_trial.h"
 #include "base/strings/string_util.h"
 #include "chrome/browser/net/prediction_options.h"
 #include "chrome/browser/prefetch/prefetch_field_trial.h"
 #include "chrome/browser/profiles/profile_io_data.h"
 #include "net/base/network_change_notifier.h"
 
 namespace prefetch {
 
 bool IsPrefetchEnabled(content::ResourceContext* resource_context) {
   DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::IO));
 
   ProfileIOData* io_data = ProfileIOData::FromResourceContext(resource_context);
 
   DCHECK(io_data);
 
-  return IsPrefetchFieldTrialEnabled() &&
-      chrome_browser_net::CanPredictNetworkActionsIO(io_data);
+  return chrome_browser_net::CanPredictNetworkActionsIO(io_data) &&
+         !DisableForFieldTrial();
 }
 
 }  // namespace prefetch