Randomly select a single rappor sample when more than one is collected.

components/rappor/rappor_metric.cc

Index: components/rappor/rappor_metric.cc
diff --git a/components/rappor/rappor_metric.cc b/components/rappor/rappor_metric.cc
index b4bd950af9d1741210b81dcdf54bbd893b1b63b2..c4c683d77a770a4f03286426d1cccf9d3c0f3a8e 100644
--- a/components/rappor/rappor_metric.cc
+++ b/components/rappor/rappor_metric.cc
@@ -5,6 +5,7 @@
 #include "components/rappor/rappor_metric.h"
 
 #include "base/logging.h"
+#include "base/rand_util.h"
 
 namespace rappor {
 
@@ -24,7 +25,13 @@ RapporMetric::RapporMetric(const std::string& metric_name,
 RapporMetric::~RapporMetric() {}
 
 void RapporMetric::AddSample(const std::string& str) {
-  bloom_filter_.AddString(str);
+  ++sample_count;

[Alexei Svitkine (slow), 2014/07/30 17:12:47]

Should be sample_count_, not sample_count.

[Steven Holte, 2014/08/04 23:30:26]

Done.

+  // Replace the previous sample with a 1 in sample_count chance so that each

[Alexei Svitkine (slow), 2014/07/30 17:12:47]

Nit: sample_count_.

[Steven Holte, 2014/08/04 23:30:26]

Done.

+  // sample has equal probability of being reported.
+  if (base::RandGenerator(sample_count) == 0) {
+    bloom_filter_.Clear();
+    bloom_filter_.AddString(str);

[Alexei Svitkine (slow), 2014/07/30 17:12:47]

Any reason why we can't just change AddString() to SetString() which does Clear
internally?

[Steven Holte, 2014/08/04 23:30:26]

Done.

+  }
 }
 
 ByteVector RapporMetric::GetReport(const std::string& secret) const {
@@ -59,4 +66,8 @@ ByteVector RapporMetric::GetReport(const std::string& secret) const {
   return *ByteVectorMerge(*fake_and_redacted_bits, zero_coins, &one_coins);
 }
 
+void RapporMetric::SetBytesForTesting(const ByteVector& bytes) {
+  bloom_filter_.SetBytesForTesting(bytes);
+}
+
 }  // namespace rappor