Disable sending persistent histograms from last session by default.

chrome/browser/metrics/chrome_metrics_service_client.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 "chrome/browser/metrics/chrome_metrics_service_client.h"
 
 #include <stddef.h>
 
 #include <set>
 #include <utility>
 #include <vector>
 
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/command_line.h"
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
+#include "base/metrics/field_trial_params.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/metrics/persistent_histogram_allocator.h"
 #include "base/metrics/statistics_recorder.h"
 #include "base/path_service.h"
 #include "base/rand_util.h"
 #include "base/strings/string16.h"
 #include "base/threading/platform_thread.h"
 #include "base/threading/sequenced_worker_pool.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "build/build_config.h"
@@ skipping 172 matching lines @@
           ->GetTaskRunnerWithShutdownBehavior(
               base::SequencedWorkerPool::CONTINUE_ON_SHUTDOWN);
 
   // Create an object to monitor files of metrics and include them in reports.
   std::unique_ptr<metrics::FileMetricsProvider> file_metrics_provider(
       new metrics::FileMetricsProvider(task_runner,
                                        g_browser_process->local_state()));
 
   base::FilePath user_data_dir;
   if (base::PathService::Get(chrome::DIR_USER_DATA, &user_data_dir)) {
-    // Register the file holding browser metrics.
+    // Reporting of persistent histograms from last session is controlled by
+    // a feature param. TODO(bcwhite): The current default is not to upload
+    // until some issues are resolved. See crbug.com/706422 for details.
+    std::string send_unreported = base::GetFieldTrialParamValueByFeature(
+        base::kPersistentHistogramsFeature, "send_unreported_metrics");
+    bool report_previous_persistent_histograms =
+        metrics_reporting_enabled && (send_unreported == "yes");
     RegisterOrRemovePreviousRunMetricsFile(
-        metrics_reporting_enabled, user_data_dir,
+        report_previous_persistent_histograms, user_data_dir,
         ChromeMetricsServiceClient::kBrowserMetricsName, task_runner,
         file_metrics_provider.get());
 
     // Register the Crashpad metrics files.
     // Register the data from the previous run if crashpad_handler didn't exit
     // cleanly.
     RegisterOrRemovePreviousRunMetricsFile(
         metrics_reporting_enabled, user_data_dir,
         kCrashpadHistogramAllocatorName, task_runner,
         file_metrics_provider.get());
@@ skipping 741 matching lines @@
     ukm_service_->Purge();
     ukm_service_->ResetClientId();
   }
   // Signal service manager to enable/disable UKM based on new state.
   UpdateRunningServices();
 }
 
 bool ChromeMetricsServiceClient::IsHistorySyncEnabledOnAllProfiles() {
   return SyncDisableObserver::IsHistorySyncEnabledOnAllProfiles();
 }