Add a histogram to debug metrics entropy source use.

components/metrics/metrics_state_manager.cc

 // Copyright 2014 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.
 
 #include "components/metrics/metrics_state_manager.h"
 
 #include "base/command_line.h"
 #include "base/guid.h"
 #include "base/metrics/histogram.h"
 #include "base/metrics/sparse_histogram.h"
@@ skipping 143 matching lines @@
   // 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.
   const int low_entropy_source_value = GetLowEntropySource();
   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_,
                                          low_entropy_source_value,
                                          kMaxLowEntropySize));
 #else
   return scoped_ptr<const base::FieldTrial::EntropyProvider>(
       new PermutedEntropyProvider(low_entropy_source_value,
                                   kMaxLowEntropySize));
 #endif
@@ skipping 100 matching lines @@
   UMA_HISTOGRAM_BOOLEAN("UMA.GeneratedLowEntropySource", true);
   low_entropy_source_ = GenerateLowEntropySource();
   local_state_->SetInteger(prefs::kMetricsLowEntropySource,
                            low_entropy_source_);
   local_state_->ClearPref(prefs::kMetricsOldLowEntropySource);
   CachingPermutedEntropyProvider::ClearCache(local_state_);
 
   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;
 
   UMA_HISTOGRAM_BOOLEAN("UMA.MetricsIDsReset", true);
 
   DCHECK(client_id_.empty());
   DCHECK_EQ(kLowEntropySourceNotSet, low_entropy_source_);
 
   local_state_->ClearPref(prefs::kMetricsClientID);
   local_state_->ClearPref(prefs::kMetricsLowEntropySource);
   local_state_->ClearPref(prefs::kMetricsResetIds);
 
   // Also clear the backed up client info.
   store_client_info_.Run(ClientInfo());
 }
 
 }  // namespace metrics