Reverting based on discussions on #chromium with shess and rsleevi

chrome/browser/history/history_field_trial.h

-// Copyright (c) 2011 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_HISTORY_HISTORY_FIELD_TRIAL_H_
-#define CHROME_BROWSER_HISTORY_HISTORY_FIELD_TRIAL_H_
-#pragma once
-
-#include <string>
-
-namespace history {
-
-class HistoryFieldTrial {
- public:
-  static void Activate();
-
-  // Returns true if history should try to use less memory.
-  static bool IsLowMemFieldTrial();
-
-  // Returns the group name as a suffix to append to histogram names for the
-  // current field trial, or the empty string if none.
-  static std::string GetGroupSuffix();
-};
-
-}  // namespace history
-
-#endif  // CHROME_BROWSER_HISTORY_HISTORY_FIELD_TRIAL_H_