Making the SHA1 entropy provider use the randomization_seed.

components/variations/entropy_provider.cc

Index: components/variations/entropy_provider.cc
diff --git a/components/variations/entropy_provider.cc b/components/variations/entropy_provider.cc
index d07277f7add2dae785bf671f364596e7f4155f10..abb4fdb4c9a1576f3bfcd29861a4b46044a86ecd 100644
--- a/components/variations/entropy_provider.cc
+++ b/components/variations/entropy_provider.cc
@@ -11,6 +11,7 @@
 #include "base/logging.h"
 #include "base/rand_util.h"
 #include "base/sha1.h"
+#include "base/strings/string_number_conversions.h"
 #include "base/sys_byteorder.h"
 #include "components/variations/metrics_util.h"
 
@@ -87,7 +88,10 @@ double SHA1EntropyProvider::GetEntropyForTrial(
   // it has been observed that this method does not result in a uniform
   // distribution given the same |trial_name|. When using such a low entropy
   // source, PermutedEntropyProvider should be used instead.
-  std::string input(entropy_source_ + trial_name);
+  std::string randomization_string =
+      randomization_seed == 0 ? trial_name
+                              : base::UintToString(randomization_seed);
+  std::string input(entropy_source_ + randomization_string);

[Alexei Svitkine (slow), 2016/11/16 06:36:48]

Nit: How about avoiding the extra string copy?

e.g.

std::string input(entropy_source_);
input.append(randomization_seed == 0 ? trial_name :
base::UintToString(randomization_seed));

This way, you don't need an extra temp randomization_string copy.
  

[jwd, 2016/11/16 16:15:45]

Done.

   unsigned char sha1_hash[base::kSHA1Length];
   base::SHA1HashBytes(reinterpret_cast<const unsigned char*>(input.c_str()),
                       input.size(),