Add a new 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.
 //
 // If a user (profile) has an explicit preference for Instant, having disabled
 // or enabled it in the Preferences page, or by having a group policy override,
 // the field trial is INACTIVE for them. There is no change in behaviour. Their
 // Instant preference is respected. Incognito profiles are also INACTIVE.
 //
 // The following mutually exclusive groups each select a small random sample of
-// the remaining users:
+// the remaining users. Instant is enabled with preloading for the EXPERIMENT
+// groups. It remains disabled, as is default, for the CONTROL groups.
 //
-// INSTANT_EXPERIMENT: Instant is enabled, but only for search. Instant is also
-//     preloaded. If the user hasn't opted to send metrics (UMA) data, they are
+// INSTANT_EXPERIMENT: Queries are issued as the user types, and previews are
+//     shown. If the user hasn't opted to send metrics (UMA) data, they are
 //     bounced back to INACTIVE.
 //
-// INSTANT_CONTROL: Instant remains disabled, as is default. If the user hasn't
-//     opted to send metrics (UMA) data, they are bounced back to INACTIVE.
+// HIDDEN_EXPERIMENT: Queries are issued as the user types, but no preview is
+//     shown until they press <Enter>. If the user hasn't opted to send metrics
+//     (UMA) data, they are bounced back to INACTIVE.
 //
-// HIDDEN_EXPERIMENT: Instant is enabled in "search only" mode, but queries are
-//     issued only when the user presses <Enter>. No previews are shown.
+// SILENT_EXPERIMENT: No queries are issued until the user presses <Enter>. No
+//     previews are shown. The user is not required to send metrics (UMA) data.
 //
-// HIDDEN_CONTROL: Instant remains disabled, as is default.
+// UMA_CONTROL: Instant is disabled. If the user hasn't opted to send metrics
+//     (UMA) data, they are bounced back to INACTIVE.
+//
+// ALL_CONTROL: Instant is disabled. The user is not required to send metrics
+//     (UMA) data.
 //
 // Users not chosen into any of the above groups are INACTIVE.
 //
 // Each non-INACTIVE group is split into two equal subgroups, to detect bias
 // between them when analyzing metrics. The subgroups are denoted by "_A" and
 // "_B" suffixes, and are treated identically for all other purposes.
 class InstantFieldTrial {
  public:
   enum Group {
     INACTIVE,
 
-    INSTANT_CONTROL_A,
-    INSTANT_CONTROL_B,
     INSTANT_EXPERIMENT_A,
     INSTANT_EXPERIMENT_B,
-
-    HIDDEN_CONTROL_A,
-    HIDDEN_CONTROL_B,
     HIDDEN_EXPERIMENT_A,
     HIDDEN_EXPERIMENT_B,
+    SILENT_EXPERIMENT_A,
+    SILENT_EXPERIMENT_B,
+
+    UMA_CONTROL_A,
+    UMA_CONTROL_B,
+    ALL_CONTROL_A,
+    ALL_CONTROL_B,
   };
 
   // Activate the field trial. Before this call, all calls to GetGroup will
   // return INACTIVE. *** MUST NOT BE CALLED MORE THAN ONCE. ***
   static void Activate();
 
   // Return the field trial group this profile belongs to.
   static Group GetGroup(Profile* profile);
 
   // Check if the user is in one of the EXPERIMENT groups.
   static bool IsExperimentGroup(Profile* profile);
 
-  // Check if the user is in the INSTANT_EXPERIMENT group.
-  static bool IsInstantExperiment(Profile* profile);
-
   // Check if the user is in the HIDDEN_EXPERIMENT group.
   static bool IsHiddenExperiment(Profile* profile);
 
+  // Check if the user is in the SILENT EXPERIMENT group.
+  static bool IsSilentExperiment(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);
 
  // Returns a string denoting the user's group, for adding as a URL param.
  static std::string GetGroupAsUrlParam(Profile* profile);
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(InstantFieldTrial);
 };
 
 #endif  // CHROME_BROWSER_INSTANT_INSTANT_FIELD_TRIAL_H_