Remove use of random_shuffle() in PermutedEntropyProvider.

components/variations/entropy_provider.cc

 // Copyright (c) 2012 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/variations/entropy_provider.h"
 
 #include <algorithm>
 #include <limits>
 #include <vector>
 
@@ skipping 32 matching lines @@
 
   return value % range;
 }
 
 void PermuteMappingUsingRandomizationSeed(uint32 randomization_seed,
                                           std::vector<uint16>* mapping) {
   for (size_t i = 0; i < mapping->size(); ++i)
     (*mapping)[i] = static_cast<uint16>(i);
 
   SeededRandGenerator generator(randomization_seed);
-  std::random_shuffle(mapping->begin(), mapping->end(), generator);
+
+  // Do a deterministic random shuffle of the mapping using |generator|.
+  //
+  // Note: This logic is identical to the following call with libstdc++ and VS:
+  //
+  //   std::random_shuffle(mapping->begin(), mapping->end(), generator);
+  //
+  // However, this is not guaranteed by the spec and some implementations (e.g.
+  // libc++) use a different algorithm. To ensure results are consistent
+  // regardless of the compiler toolchain used, use our own version.
+  for (size_t i = 1; i < mapping->size(); ++i) {
+    // Pick an element in mapping[:i+1] with which to exchange mapping[i].
+    size_t j = generator(i + 1);
+    std::swap((*mapping)[i], (*mapping)[j]);
+  }
 }
 
 }  // namespace internal
 
 SHA1EntropyProvider::SHA1EntropyProvider(const std::string& entropy_source)
     : entropy_source_(entropy_source) {
 }
 
 SHA1EntropyProvider::~SHA1EntropyProvider() {
 }
@@ skipping 46 matching lines @@
 }
 
 uint16 PermutedEntropyProvider::GetPermutedValue(
     uint32 randomization_seed) const {
   std::vector<uint16> mapping(low_entropy_source_max_);
   internal::PermuteMappingUsingRandomizationSeed(randomization_seed, &mapping);
   return mapping[low_entropy_source_];
 }
 
 }  // namespace metrics