Add about flag for offline page experiment

components/offline_pages/offline_page_feature.cc

 // Copyright 2015 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 "components/offline_pages/offline_page_feature.h"
 
 #include <string>
 
+#include "base/command_line.h"
 #include "base/metrics/field_trial.h"
+#include "components/offline_pages/offline_page_switches.h"
 
 #if defined(OS_ANDROID)
 
 namespace offline_pages {
 
 namespace {
 const char kOfflinePagesFieldTrialName[] = "OfflinePages";
 const char kOfflinePagesFieldTrialEnabledGroupName[] = "Enabled";
 }  // namespace
 
 bool IsOfflinePagesEnabled() {
+  if (base::CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kEnableOfflinePages)) {
+    return true;
+  }
+  if (base::CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kDisableOfflinePages)) {
+    return false;
+  }
+
   std::string group_name =
       base::FieldTrialList::FindFullName(kOfflinePagesFieldTrialName);
   return group_name == kOfflinePagesFieldTrialEnabledGroupName;
 }
 
 }  // namespace offline_pages
 
 #endif