Modify rappor parameters.

components/rappor/rappor_parameters.h

 // Copyright 2014 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 COMPONENTS_RAPPOR_RAPPOR_PARAMETERS_H_
 #define COMPONENTS_RAPPOR_RAPPOR_PARAMETERS_H_
 
 #include <string>
 
 namespace rappor {
 
 enum Probability {
   PROBABILITY_75,    // 75%
   PROBABILITY_50,    // 50%
+  PROBABILITY_25,    // 25%
 };
 
 // An object describing a rappor metric and the parameters used to generate it.
 //
 // For a full description of the rappor metrics, see
 // http://www.chromium.org/developers/design-documents/rappor
 struct RapporParameters {
   // Get a string representing the parameters, for DCHECK_EQ.
   std::string ToString() const;
 
+  // The maximum number of cohorts we divide clients into.
+  static const int kMaxCohorts = 512;
+  // The number of cohorts to divide the reports for this metric into.
+  int num_cohorts;
+
   // The number of bytes stored in the Bloom filter.
   int bloom_filter_size_bytes;
   // The number of hash functions used in the Bloom filter.
   int bloom_filter_hash_function_count;
 
   // The probability that a bit will be redacted with fake data.
   Probability fake_prob;
   // The probability that a fake bit will be a one.
   Probability fake_one_prob;
 
   // The probability that a one bit in the redacted data reports as one.
   Probability one_coin_prob;
   // The probability that a zero bit in the redacted data reports as one.
   Probability zero_coin_prob;
 };
 
 }  // namespace rappor
 
 #endif  // COMPONENTS_RAPPOR_RAPPOR_PARAMETERS_H_