Use low entropy for studies that send experiment IDs to Google properties.

components/variations/service/variations_service.cc

Index: components/variations/service/variations_service.cc
diff --git a/components/variations/service/variations_service.cc b/components/variations/service/variations_service.cc
index d1f4cf3d7004042d5c82d5126f36a1a5c8889601..eb3695c326998fb509b8b800a26cefa1f4988e88 100644
--- a/components/variations/service/variations_service.cc
+++ b/components/variations/service/variations_service.cc
@@ -336,6 +336,9 @@ bool VariationsService::CreateTrialsFromSeed(base::FeatureList* feature_list) {
 
   const std::string latest_country =
       local_state_->GetString(prefs::kVariationsCountry);
+
+  std::unique_ptr<const base::FieldTrial::EntropyProvider> low_entropy_provider(
+      GetLowEntropyProvider());
   // Note that passing |&ui_string_overrider_| via base::Unretained below is
   // safe because the callback is executed synchronously. It is not possible
   // to pass UIStringOverrider itself to VariationSeedProcesor as variations
@@ -347,7 +350,7 @@ bool VariationsService::CreateTrialsFromSeed(base::FeatureList* feature_list) {
       LoadPermanentConsistencyCountry(current_version, latest_country),
       base::Bind(&UIStringOverrider::OverrideUIString,
                  base::Unretained(&ui_string_overrider_)),
-      feature_list);
+      feature_list, low_entropy_provider.get());
 
   const base::Time now = base::Time::Now();
 
@@ -595,6 +598,11 @@ bool VariationsService::StoreSeed(const std::string& seed_data,
   return true;
 }
 
+std::unique_ptr<const base::FieldTrial::EntropyProvider>
+VariationsService::GetLowEntropyProvider() {

[Alexei Svitkine (slow), 2016/05/17 16:31:35]

Nit: CreateLowEntropyProvider.

Although, maybe no need to have this wrapper at all?

Or is it here just to make the tests happy? If so, mention it in the declaration
in the header.

[jwd, 2016/05/18 13:24:18]

Done.

Yeah, it's for the tests.

+  return state_manager_->CreateLowEntropyProvider();
+}
+
 bool VariationsService::LoadSeed(VariationsSeed* seed) {
   return seed_store_.LoadSeed(seed);
 }
@@ -740,7 +748,7 @@ void VariationsService::PerformSimulationWithVersion(
   const base::ElapsedTimer timer;
 
   std::unique_ptr<const base::FieldTrial::EntropyProvider> entropy_provider =
-      state_manager_->CreateEntropyProvider();
+      state_manager_->CreateDefaultEntropyProvider();
   variations::VariationsSeedSimulator seed_simulator(*entropy_provider);
 
   const std::string latest_country =