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

components/rappor/bloom_filter.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/bloom_filter.h"
 
 #include "base/logging.h"
 #include "third_party/smhasher/src/City.h"
 
 namespace rappor {
 
 BloomFilter::BloomFilter(uint32_t bytes_size,
                          uint32_t hash_function_count,
                          uint32_t hash_seed_offset)
     : bytes_(bytes_size),
       hash_function_count_(hash_function_count),
       hash_seed_offset_(hash_seed_offset) {
   DCHECK_GT(bytes_size, 0u);
 }
 
 BloomFilter::~BloomFilter() {}
 
-void BloomFilter::AddString(const std::string& str) {
+void BloomFilter::SetString(const std::string& str) {
+  for (size_t i = 0; i < bytes_.size(); ++i) {
+    bytes_[i] = 0;
+  }
   for (size_t i = 0; i < hash_function_count_; ++i) {
     // Using CityHash here because we have support for it in Dremel.  Many hash
     // functions, such as MD5, SHA1, or Murmur, would probably also work.
     uint32_t index =
         CityHash64WithSeed(str.data(), str.size(), hash_seed_offset_ + i);
     // Note that the "bytes" are uint8_t, so they are always 8-bits.
     uint32_t byte_index = (index / 8) % bytes_.size();
     uint32_t bit_index = index % 8;
     bytes_[byte_index] |= 1 << bit_index;
   }
 }
 
+void BloomFilter::SetBytesForTesting(const ByteVector& bytes) {
+  DCHECK_EQ(bytes_.size(), bytes.size());
+  for (size_t i = 0; i < bytes_.size(); ++i) {
+    bytes_[i] = bytes[i];
+  }
+}
+
 }  // namespace rappor