Restrict transmission of external exp ids to signed in users.

chrome/browser/android/metrics/uma_session_stats.cc

Index: chrome/browser/android/metrics/uma_session_stats.cc
diff --git a/chrome/browser/android/metrics/uma_session_stats.cc b/chrome/browser/android/metrics/uma_session_stats.cc
index d2ce89b1769eb5fce2eeb861b258f1fcf152a4d6..c318ddbde290a837b7cddf11af1d815616888bd1 100644
--- a/chrome/browser/android/metrics/uma_session_stats.cc
+++ b/chrome/browser/android/metrics/uma_session_stats.cc
@@ -168,8 +168,11 @@ static void RegisterExternalExperiment(
   active_group.name = metrics::HashName(trial_name_utf8);
   for (int experiment_id : experiment_ids) {
     active_group.group = metrics::HashName(base::IntToString(experiment_id));
+    // Since external experiments are not based on Chrome's low entropy source,
+    // they are only sent to Google web properties for signed in users to make
+    // sure that this couldn't be used to identify a user that's not signed in.
     variations::AssociateGoogleVariationIDForceHashes(
-        variations::GOOGLE_WEB_PROPERTIES, active_group,
+        variations::GOOGLE_WEB_PROPERTIES_SIGNED_IN, active_group,
         static_cast<variations::VariationID>(experiment_id));
     group_name_hashes.push_back(active_group.group);
   }