Support experiment configurations with/without stability metrics.

chrome/browser/chrome_browser_field_trials.cc

 // Copyright (c) 2012 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/chrome_browser_field_trials.h"
 
 #include <string>
 
 #include "base/command_line.h"
 #include "base/feature_list.h"
 #include "base/files/file_util.h"
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram_base.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/metrics/persistent_histogram_allocator.h"
 #include "base/path_service.h"
 #include "base/strings/string_util.h"
 #include "base/time/time.h"
 #include "build/build_config.h"
 #include "chrome/browser/metrics/chrome_metrics_service_client.h"
 #include "chrome/browser/metrics/chrome_metrics_services_manager_client.h"
 #include "chrome/browser/tracing/background_tracing_field_trial.h"
 #include "chrome/common/channel_info.h"
 #include "chrome/common/chrome_paths.h"
 #include "chrome/common/chrome_switches.h"
+#include "components/metrics/file_metrics_provider.h"
 #include "components/metrics/metrics_pref_names.h"
 #include "components/variations/variations_associated_data.h"
 
 #if defined(OS_ANDROID)
 #include "chrome/browser/chrome_browser_field_trials_mobile.h"
 #else
 #include "chrome/browser/chrome_browser_field_trials_desktop.h"
 #endif
 
 namespace {
@@ skipping 37 matching lines @@
   const size_t kAllocSize = 3 << 20;     // 3 MiB
   const uint32_t kAllocId = 0x935DDD43;  // SHA1(BrowserMetrics)
   std::string storage = variations::GetVariationParamValueByFeature(
       base::kPersistentHistogramsFeature, "storage");
   if (storage == "MappedFile") {
     // Create global allocator with the "active" file.
     base::GlobalHistogramAllocator::CreateWithFile(
         active_file, kAllocSize, kAllocId,
         ChromeMetricsServiceClient::kBrowserMetricsName);
     result = MAPPED_FILE_SUCCESS;
+    // Some configurations don't return unreported metrics from the previous
+    // run (otherwise known as "stability metrics").
+    std::string unreported = variations::GetVariationParamValueByFeature(
+        base::kPersistentHistogramsFeature, "send_unreported_metrics");
+    metrics::FileMetricsProvider::SetStabilityMetricsEnabled(
+        unreported == "yes");

[Alexei Svitkine (slow), 2016/11/24 21:27:58]

This would change the meaning of the existing groups.

How about making the new param be in the negative (e.g.
disable_stability_uploads or something)?

[bcwhite, 2016/11/25 18:51:57]

I've never liked the double negatives that occur that way but there's an easy
fix:  != "no".

   } else if (storage == "LocalMemory") {
     // Use local memory for storage even though it will not persist across
     // an unclean shutdown.
     base::GlobalHistogramAllocator::CreateWithLocalMemory(
         kAllocSize, kAllocId, ChromeMetricsServiceClient::kBrowserMetricsName);
     result = LOCAL_MEMORY_SUCCESS;
   } else {
     // Persistent metric storage is disabled.
     return;
   }
@@ skipping 56 matching lines @@
     bool has_seed,
     base::FeatureList* feature_list) {
   CreateFallbackSamplingTrialIfNeeded(has_seed, feature_list);
 }
 
 void ChromeBrowserFieldTrials::InstantiateDynamicTrials() {
   // Persistent histograms must be enabled as soon as possible.
   InstantiatePersistentHistograms();
   tracing::SetupBackgroundTracingFieldTrial();
 }