Record the first recorded entropy source instead of the last.

chrome/browser/metrics/metrics_service.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.
 
 //------------------------------------------------------------------------------
 // Description of the life cycle of a instance of MetricsService.
 //
 //  OVERVIEW
 //
 // A MetricsService instance is typically created at application startup.  It
@@ skipping 531 matching lines @@
 std::string MetricsService::GetEntropySource(bool reporting_will_be_enabled) {
   // For metrics reporting-enabled users, we combine the client ID and low
   // entropy source to get the final entropy source. Otherwise, only use the low
   // entropy source.
   // This has two useful properties:
   //  1) It makes the entropy source less identifiable for parties that do not
   //     know the low entropy source.
   //  2) It makes the final entropy source resettable.
   std::string low_entropy_source = base::IntToString(GetLowEntropySource());
   if (reporting_will_be_enabled) {
-    entropy_source_returned_ = LAST_ENTROPY_HIGH;
+    if (entropy_source_returned_ == LAST_ENTROPY_NONE)
+      entropy_source_returned_ = LAST_ENTROPY_HIGH;
+    DCHECK_EQ(LAST_ENTROPY_HIGH, entropy_source_returned_);
     return client_id_ + low_entropy_source;
   }
-  entropy_source_returned_ = LAST_ENTROPY_LOW;
+  if (entropy_source_returned_ == LAST_ENTROPY_NONE)
+    entropy_source_returned_ = LAST_ENTROPY_LOW;
+  DCHECK_EQ(LAST_ENTROPY_LOW, entropy_source_returned_);
   return low_entropy_source;
 }
 
 void MetricsService::ForceClientIdCreation() {
   if (!client_id_.empty())
     return;
   PrefService* pref = g_browser_process->local_state();
   client_id_ = pref->GetString(prefs::kMetricsClientID);
   if (!client_id_.empty())
     return;
@@ skipping 1343 matching lines @@
   if (local_state) {
     const PrefService::Preference* uma_pref =
         local_state->FindPreference(prefs::kMetricsReportingEnabled);
     if (uma_pref) {
       bool success = uma_pref->GetValue()->GetAsBoolean(&result);
       DCHECK(success);
     }
   }
   return result;
 }