Resetting metrics ids on clump detection.

chrome/browser/metrics/metrics_service.cc

Index: chrome/browser/metrics/metrics_service.cc
diff --git a/chrome/browser/metrics/metrics_service.cc b/chrome/browser/metrics/metrics_service.cc
index a313c4514051b636009db4616c10559f98a64ca5..7155c40925380cdcf794a80a7659067afcbe221d 100644
--- a/chrome/browser/metrics/metrics_service.cc
+++ b/chrome/browser/metrics/metrics_service.cc
@@ -435,6 +435,7 @@ class MetricsMemoryDetails : public MemoryDetails {
 // static
 void MetricsService::RegisterPrefs(PrefRegistrySimple* registry) {
   DCHECK(IsSingleThreaded());
+  registry->RegisterBooleanPref(prefs::kMetricsResetIds, false);
   registry->RegisterStringPref(prefs::kMetricsClientID, std::string());
   registry->RegisterIntegerPref(prefs::kMetricsLowEntropySource,
                                 kLowEntropySourceNotSet);
@@ -521,7 +522,8 @@ void MetricsService::DiscardOldStabilityStats(PrefService* local_state) {
 }
 
 MetricsService::MetricsService()
-    : recording_active_(false),
+    : metrics_ids_reset_check_performed_(false),
+      recording_active_(false),
       reporting_active_(false),
       test_mode_active_(false),
       state_(INITIALIZED),
@@ -633,6 +635,9 @@ MetricsService::CreateEntropyProvider(ReportingState reporting_state) {
 void MetricsService::ForceClientIdCreation() {
   if (!client_id_.empty())
     return;
+
+  ResetMetricsIDsIfNecessary();
+
   PrefService* pref = g_browser_process->local_state();
   client_id_ = pref->GetString(prefs::kMetricsClientID);
   if (!client_id_.empty())
@@ -1185,6 +1190,26 @@ void MetricsService::GetUptimes(PrefService* pref,
   }
 }
 
+void MetricsService::ResetMetricsIDsIfNecessary() {
+  if (metrics_ids_reset_check_performed_)
+    return;
+
+  metrics_ids_reset_check_performed_ = true;
+
+  PrefService* local_state = g_browser_process->local_state();
+  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);
+}
+
 int MetricsService::GetLowEntropySource() {
   // Note that the default value for the low entropy source and the default pref
   // value are both kLowEntropySourceNotSet, which is used to identify if the
@@ -1192,6 +1217,8 @@ int MetricsService::GetLowEntropySource() {
   if (low_entropy_source_ != kLowEntropySourceNotSet)
     return low_entropy_source_;
 
+  ResetMetricsIDsIfNecessary();
+
   PrefService* local_state = g_browser_process->local_state();
   const CommandLine* command_line(CommandLine::ForCurrentProcess());
   // Only try to load the value from prefs if the user did not request a reset.