Retrieve client_id from GoogleUpdateSettings when its missing from Local State.

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 3b71976581b30d789d37c05ea2f0cb1d86bfa658..3fe2f176f82edae86d126c5aee5c5eaf13168b20 100644
--- a/components/metrics/metrics_state_manager.cc
+++ b/components/metrics/metrics_state_manager.cc
@@ -45,9 +45,13 @@ bool MetricsStateManager::instance_exists_ = false;
 
 MetricsStateManager::MetricsStateManager(
     PrefService* local_state,
-    const base::Callback<bool(void)>& is_reporting_enabled_callback)
+    const base::Callback<bool(void)>& is_reporting_enabled_callback,
+    const StoreClientInfoCallback& store_client_info,
+    const LoadClientInfoCallback& retrieve_client_info)
     : local_state_(local_state),
       is_reporting_enabled_callback_(is_reporting_enabled_callback),
+      store_client_info_(store_client_info),
+      load_client_info_(retrieve_client_info),
       low_entropy_source_(kLowEntropySourceNotSet),
       entropy_source_returned_(ENTROPY_SOURCE_NONE) {
   ResetMetricsIDsIfNecessary();
@@ -72,9 +76,52 @@ void MetricsStateManager::ForceClientIdCreation() {
     return;
 
   client_id_ = local_state_->GetString(prefs::kMetricsClientID);
-  if (!client_id_.empty())
+  if (!client_id_.empty()) {
+    // It is technically sufficient to only save a backup of the client id when
+    // it is initially generated below, but since the backup was only introduced
+    // in M38, seed it explicitly from here for some time.
+    BackupCurrentClientInfo();
+    return;
+  }
+
+  scoped_ptr<ClientInfo> client_info_backup = load_client_info_.Run();
+  if (client_info_backup) {
+    client_id_ = client_info_backup->client_id;
+
+    const base::Time now(base::Time::Now());
+
+    // Save the recovered client id and also try to reinstantiate the backup
+    // values for the dates corresponding with that client id in order to avoid
+    // weird scenarios where we could report an old client id with a recent
+    // install date.
+    local_state_->SetString(prefs::kMetricsClientID, client_id_);
+    local_state_->SetInt64(prefs::kInstallDate,
+                           client_info_backup->installation_date ?
+                               client_info_backup->installation_date :
+                               now.ToTimeT());
+    local_state_->SetInt64(prefs::kMetricsReportingEnabledTimestamp,
+                           client_info_backup->reporting_enabled_date ?
+                               client_info_backup->reporting_enabled_date :
+                               now.ToTimeT());
+
+    base::TimeDelta recovered_installation_age;
+    if (client_info_backup->installation_date != 0) {
+      recovered_installation_age =
+          now - base::Time::FromTimeT(client_info_backup->installation_date);
+    }
+    UMA_HISTOGRAM_CUSTOM_TIMES("UMA.ClientIdBackupRecoveredWithAge",
+                               recovered_installation_age,
+                               base::TimeDelta::FromHours(0),
+                               base::TimeDelta::FromDays(365),
+                               100);
+
+    // Flush the backup back to persistent storage in case we re-generated
+    // missing data above.
+    BackupCurrentClientInfo();
     return;
+  }
 
+  // Failing attempts at getting an existing client ID, generate a new one.
   client_id_ = base::GenerateGUID();
   local_state_->SetString(prefs::kMetricsClientID, client_id_);
 
@@ -86,6 +133,8 @@ void MetricsStateManager::ForceClientIdCreation() {
     UMA_HISTOGRAM_BOOLEAN("UMA.ClientIdMigrated", true);
   }
   local_state_->ClearPref(prefs::kMetricsOldClientID);
+
+  BackupCurrentClientInfo();
 }
 
 void MetricsStateManager::CheckForClonedInstall(
@@ -141,12 +190,16 @@ MetricsStateManager::CreateEntropyProvider() {
 // static
 scoped_ptr<MetricsStateManager> MetricsStateManager::Create(
     PrefService* local_state,
-    const base::Callback<bool(void)>& is_reporting_enabled_callback) {
+    const base::Callback<bool(void)>& is_reporting_enabled_callback,
+    const StoreClientInfoCallback& store_client_info,
+    const LoadClientInfoCallback& retrieve_client_info) {
   scoped_ptr<MetricsStateManager> result;
   // Note: |instance_exists_| is updated in the constructor and destructor.
   if (!instance_exists_) {
-    result.reset(
-        new MetricsStateManager(local_state, is_reporting_enabled_callback));
+    result.reset(new MetricsStateManager(local_state,
+                                         is_reporting_enabled_callback,
+                                         store_client_info,
+                                         retrieve_client_info));
   }
   return result.Pass();
 }
@@ -168,6 +221,15 @@ void MetricsStateManager::RegisterPrefs(PrefRegistrySimple* registry) {
   registry->RegisterIntegerPref(prefs::kMetricsOldLowEntropySource, 0);
 }
 
+void MetricsStateManager::BackupCurrentClientInfo() {
+  ClientInfo client_info;
+  client_info.client_id = client_id_;
+  client_info.installation_date = local_state_->GetInt64(prefs::kInstallDate);
+  client_info.reporting_enabled_date =
+      local_state_->GetInt64(prefs::kMetricsReportingEnabledTimestamp);
+  store_client_info_.Run(client_info);
+}
+
 int MetricsStateManager::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