[Prerender] Get the prerender mode from Finch field trial.

chrome/browser/chrome_browser_field_trials_mobile.h

 // 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.
 
 #ifndef CHROME_BROWSER_CHROME_BROWSER_FIELD_TRIALS_MOBILE_H_
 #define CHROME_BROWSER_CHROME_BROWSER_FIELD_TRIALS_MOBILE_H_
 
-#include "base/time/time.h"
-
-namespace base {
-class CommandLine;
-}
-
 namespace chrome {
 
 // Sets up mobile-only field trials.
 // Add an invocation of your field trial init function to this method, or to
 // SetupFieldTrials in chrome_browser_field_trials.cc if it is for all
 // platforms.
-void SetupMobileFieldTrials(const base::CommandLine& parsed_command_line);
+void SetupMobileFieldTrials();
 
 }  // namespace chrome
 
 #endif  // CHROME_BROWSER_CHROME_BROWSER_FIELD_TRIALS_MOBILE_H_