Add a histogram to debug metrics entropy source use.

components/metrics/metrics_state_manager.cc

Index: components/metrics/metrics_state_manager.cc
diff --git a/components/metrics/metrics_state_manager.cc b/components/metrics/metrics_state_manager.cc
index 7e98bdbff01c2db8c5bccf340ff475ffc4ce3c07..477751bd8894fe6fc418e5ee5fae82a00abc9784 100644
--- a/components/metrics/metrics_state_manager.cc
+++ b/components/metrics/metrics_state_manager.cc
@@ -161,17 +161,14 @@ MetricsStateManager::CreateEntropyProvider() {
   UMA_HISTOGRAM_SPARSE_SLOWLY("UMA.LowEntropySourceValue",
                               low_entropy_source_value);
   if (IsMetricsReportingEnabled()) {
-    if (entropy_source_returned_ == ENTROPY_SOURCE_NONE)
-      entropy_source_returned_ = ENTROPY_SOURCE_HIGH;
+    UpdateEntropySourceReturnedValue(ENTROPY_SOURCE_HIGH);
     const std::string high_entropy_source =
         client_id_ + base::IntToString(low_entropy_source_value);
     return scoped_ptr<const base::FieldTrial::EntropyProvider>(
         new SHA1EntropyProvider(high_entropy_source));
   }
 
-  if (entropy_source_returned_ == ENTROPY_SOURCE_NONE)
-    entropy_source_returned_ = ENTROPY_SOURCE_LOW;
-
+  UpdateEntropySourceReturnedValue(ENTROPY_SOURCE_LOW);
 #if defined(OS_ANDROID) || defined(OS_IOS)
   return scoped_ptr<const base::FieldTrial::EntropyProvider>(
       new CachingPermutedEntropyProvider(local_state_,
@@ -292,6 +289,16 @@ int MetricsStateManager::GetLowEntropySource() {
   return low_entropy_source_;
 }
 
+void MetricsStateManager::UpdateEntropySourceReturnedValue(
+    EntropySourceType type) {
+  if (entropy_source_returned_ != ENTROPY_SOURCE_NONE)
+    return;
+
+  entropy_source_returned_ = type;
+  UMA_HISTOGRAM_ENUMERATION("UMA.EntropySourceType", type,
+                            ENTROPY_SOURCE_ENUM_SIZE);
+}
+
 void MetricsStateManager::ResetMetricsIDsIfNecessary() {
   if (!local_state_->GetBoolean(prefs::kMetricsResetIds))
     return;