Create a mechanism for reporting rappor metrics from non-UMA

components/rappor/rappor_metric.cc

 // 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.
 
 #include "components/rappor/rappor_metric.h"
 
 #include "base/logging.h"
 #include "base/rand_util.h"
 
 namespace rappor {
 
 RapporMetric::RapporMetric(const std::string& metric_name,
                            const RapporParameters& parameters,
                            int32_t cohort_seed)
     : metric_name_(metric_name),
       parameters_(parameters),
       sample_count_(0),
       bloom_filter_(parameters.bloom_filter_size_bytes,
                     parameters.bloom_filter_hash_function_count,
                     (cohort_seed % parameters.num_cohorts) *
                         parameters.bloom_filter_hash_function_count) {
   DCHECK_GE(cohort_seed, 0);
   DCHECK_LT(cohort_seed, RapporParameters::kMaxCohorts);
+  // Since cohort_seed is in the range [0, kMaxCohorts), num_cohorts should
+  // divide kMaxCohorts for each cohort to have equal weight.
+  DCHECK_EQ(RapporParameters::kMaxCohorts % parameters.num_cohorts, 0);

[Alexei Svitkine (slow), 2014/10/03 20:28:50]

Nit: Expected value goes on the left for DCHECK_EQ.

[Steven Holte, 2014/10/03 21:41:11]

Done.

 }
 
 RapporMetric::~RapporMetric() {}
 
 void RapporMetric::AddSample(const std::string& str) {
   ++sample_count_;
   // Replace the previous sample with a 1 in sample_count_ chance so that each
   // sample has equal probability of being reported.
   if (base::RandGenerator(sample_count_) == 0) {
     bloom_filter_.SetString(str);
@@ skipping 30 matching lines @@
   // the outcome of flipping a zero coin for the zero bits in that data, and of
   // flipping a one coin for the one bits in that data, as the final report.
   return *ByteVectorMerge(*fake_and_redacted_bits, zero_coins, &one_coins);
 }
 
 void RapporMetric::SetBytesForTesting(const ByteVector& bytes) {
   bloom_filter_.SetBytesForTesting(bytes);
 }
 
 }  // namespace rappor