Revert 94073 (broke a ton of tests) - Introduce a field trial for Instant.

chrome/browser/instant/instant_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_INSTANT_INSTANT_FIELD_TRIAL_H_
-#define CHROME_BROWSER_INSTANT_INSTANT_FIELD_TRIAL_H_
-
-#include <string>
-
-#include "base/basictypes.h"
-
-class Profile;
-
-// This class manages the Instant field trial. Each user is in exactly one of
-// three field trial groups: Inactive, Control or Experiment.
-// - Inactive users are those who have played with the Instant option in the
-//   Preferences page, or those for whom group policy provides an override, or
-//   those with an incognito profile, etc. The field trial is inactive for such
-//   users, so their Instant preference setting is respected.
-// - Control and Experiment are all the other users, i.e., those who have never
-//   touched the Preferences option. Some percentage of these users are chosen
-//   into the Experiment group and get Instant enabled automatically. The rest
-//   fall into the Control group; for them, Instant remains disabled by default.
-// - Control and Experiment are further split into two subgroups each, in order
-//   to detect bias between them (when analyzing metrics). The subgroups are
-//   treated identically for all other purposes.
-class InstantFieldTrial {
- public:
-  enum Group {
-    INACTIVE,
-    CONTROL1,
-    CONTROL2,
-    EXPERIMENT1,
-    EXPERIMENT2,
-  };
-  static Group GetGroup(Profile* profile);
-
-  // Check if the group is either of the two experiment subgroups.
-  static bool IsExperimentGroup(Profile* profile);
-
-  // Returns a string describing the user's group. Can be added to histogram
-  // names, to split histograms by field trial groups.
-  static std::string GetGroupName(Profile* profile);
-
- private:
-  DISALLOW_IMPLICIT_CONSTRUCTORS(InstantFieldTrial);
-};
-
-#endif  // CHROME_BROWSER_INSTANT_INSTANT_FIELD_TRIAL_H_