Add a URL param to indicate group selection in Instant field trial.

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"
@@ skipping 32 matching lines @@
   // Return the field trial group this profile belongs to.
   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);
 
+ // 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_