Move EntropyProvider Source From MetricsService to MetricsServicesManager

This paves the way to allow Variations initialization to occur without
MetricsService initialization. Deferring MetricsService inititalization
is needed for the Browser Task Scheduler work as the underlying
metrics providers will post asynchronous tasks.

BUG=636518

Review-Url: https://codereview.chromium.org/2333283005
Cr-Commit-Position: refs/heads/master@{#418866}

chrome/browser/chrome_browser_main.cc

@@ -794,17 +794,14 @@ ChromeBrowserMainParts::~ChromeBrowserMainParts() {
 // This will be called after the command-line has been mutated by about:flags
 void ChromeBrowserMainParts::SetupMetricsAndFieldTrials() {
   TRACE_EVENT0("startup", "ChromeBrowserMainParts::SetupMetricsAndFieldTrials");
-  // Must initialize metrics after labs have been converted into switches,
-  // but before field trials are set up (so that client ID is available for
-  // one-time randomized field trials).
 
   // Initialize FieldTrialList to support FieldTrials that use one-time
   // randomization.
-  metrics::MetricsService* metrics = browser_process_->metrics_service();
-
   DCHECK(!field_trial_list_);
   field_trial_list_.reset(
-      new base::FieldTrialList(metrics->CreateEntropyProvider().release()));
+      new base::FieldTrialList(browser_process_->GetMetricsServicesManager()
+                                   ->CreateEntropyProvider()
+                                   .release()));
 
   const base::CommandLine* command_line =
       base::CommandLine::ForCurrentProcess();
@@ -845,6 +842,11 @@ void ChromeBrowserMainParts::SetupMetricsAndFieldTrials() {
       about_flags::RegisterAllFeatureVariationParameters(
           &flags_storage, feature_list.get());
 
+  // Must initialize metrics after about:flags have been converted into
+  // switches, but before field trials are set up (so that client ID is
+  // available for one-time randomized field trials).
+  metrics::MetricsService* metrics = browser_process_->metrics_service();
+
   variations::VariationsHttpHeaderProvider* http_header_provider =
       variations::VariationsHttpHeaderProvider::GetInstance();
   // Force the variation ids selected in chrome://flags and/or specified using

chrome/browser/metrics/chrome_metrics_services_manager_client.cc

@@ -210,6 +210,11 @@ ChromeMetricsServicesManagerClient::CreateMetricsServiceClient() {
   return ChromeMetricsServiceClient::Create(GetMetricsStateManager());
 }
 
+std::unique_ptr<const base::FieldTrial::EntropyProvider>
+ChromeMetricsServicesManagerClient::CreateEntropyProvider() {
+  return GetMetricsStateManager()->CreateDefaultEntropyProvider();
+}
+
 net::URLRequestContextGetter*
 ChromeMetricsServicesManagerClient::GetURLRequestContext() {
   return g_browser_process->system_request_context();

chrome/browser/metrics/chrome_metrics_services_manager_client.h

@@ -9,6 +9,7 @@
 
 #include "base/feature_list.h"
 #include "base/macros.h"
+#include "base/metrics/field_trial.h"
 #include "base/threading/thread_checker.h"
 #include "chrome/browser/safe_browsing/safe_browsing_service.h"
 #include "components/metrics_services_manager/metrics_services_manager_client.h"
@@ -64,6 +65,8 @@ class ChromeMetricsServicesManagerClient
       override;
   std::unique_ptr<metrics::MetricsServiceClient> CreateMetricsServiceClient()
       override;
+  std::unique_ptr<const base::FieldTrial::EntropyProvider>
+  CreateEntropyProvider() override;
   net::URLRequestContextGetter* GetURLRequestContext() override;
   bool IsSafeBrowsingEnabled(const base::Closure& on_update_callback) override;
   bool IsMetricsReportingEnabled() override;

components/metrics/metrics_service.cc

@@ -361,13 +361,6 @@ bool MetricsService::WasLastShutdownClean() const {
   return clean_exit_beacon_.exited_cleanly();
 }
 
-std::unique_ptr<const base::FieldTrial::EntropyProvider>
-MetricsService::CreateEntropyProvider() {
-  // TODO(asvitkine): Refactor the code so that MetricsService does not expose
-  // this method.
-  return state_manager_->CreateDefaultEntropyProvider();
-}
-
 void MetricsService::EnableRecording() {
   DCHECK(IsSingleThreaded());
 

components/metrics/metrics_service.h

@@ -124,16 +124,6 @@ class MetricsService : public base::HistogramFlattener {
   // Returns true if the last session exited cleanly.
   bool WasLastShutdownClean() const;
 
-  // Returns the preferred entropy provider used to seed persistent activities
-  // based on whether or not metrics reporting will be permitted on this client.
-  //
-  // If metrics reporting is enabled, this method returns an entropy provider
-  // that has a high source of entropy, partially based on the client ID.
-  // Otherwise, it returns an entropy provider that is based on a low entropy
-  // source.
-  std::unique_ptr<const base::FieldTrial::EntropyProvider>
-  CreateEntropyProvider();
-
   // At startup, prefs needs to be called with a list of all the pref names and
   // types we'll be using.
   static void RegisterPrefs(PrefRegistrySimple* registry);

components/metrics_services_manager/metrics_services_manager.cc

@@ -24,6 +24,11 @@ MetricsServicesManager::MetricsServicesManager(
 
 MetricsServicesManager::~MetricsServicesManager() {}
 
+std::unique_ptr<const base::FieldTrial::EntropyProvider>
+MetricsServicesManager::CreateEntropyProvider() {
+  return client_->CreateEntropyProvider();
+}
+
 metrics::MetricsService* MetricsServicesManager::GetMetricsService() {
   DCHECK(thread_checker_.CalledOnValidThread());
   return GetMetricsServiceClient()->GetMetricsService();

components/metrics_services_manager/metrics_services_manager.h

@@ -8,6 +8,7 @@
 #include <memory>
 
 #include "base/macros.h"
+#include "base/metrics/field_trial.h"
 #include "base/threading/thread_checker.h"
 
 namespace base {
@@ -42,6 +43,16 @@ class MetricsServicesManager {
       std::unique_ptr<MetricsServicesManagerClient> client);
   virtual ~MetricsServicesManager();
 
+  // Returns the preferred entropy provider used to seed persistent activities
+  // based on whether or not metrics reporting is permitted on this client.
+  //
+  // If there's consent to report metrics, this method returns an entropy
+  // provider that has a high source of entropy, partially based on the client
+  // ID. Otherwise, it returns an entropy provider that is based on a low
+  // entropy source.
+  std::unique_ptr<const base::FieldTrial::EntropyProvider>
+  CreateEntropyProvider();
+
   // Returns the MetricsService, creating it if it hasn't been created yet (and
   // additionally creating the MetricsServiceClient in that case).
   metrics::MetricsService* GetMetricsService();

components/metrics_services_manager/metrics_services_manager_client.h

@@ -8,6 +8,7 @@
 #include <memory>
 
 #include "base/callback_forward.h"
+#include "base/metrics/field_trial.h"
 
 namespace metrics {
 class MetricsServiceClient;
@@ -39,6 +40,8 @@ class MetricsServicesManagerClient {
   CreateVariationsService() = 0;
   virtual std::unique_ptr<metrics::MetricsServiceClient>
   CreateMetricsServiceClient() = 0;
+  virtual std::unique_ptr<const base::FieldTrial::EntropyProvider>
+  CreateEntropyProvider() = 0;
 
   // Returns the URL request context in which the metrics services should
   // operate.

ios/chrome/browser/ios_chrome_main_parts.mm

@@ -196,15 +196,13 @@ void IOSChromeMainParts::SetUpMetricsAndFieldTrials() {
   base::SetRecordActionTaskRunner(
       web::WebThread::GetTaskRunnerForThread(web::WebThread::UI));
 
-  // Must initialize metrics after labs have been converted into switches,
-  // but before field trials are set up (so that client ID is available for
-  // one-time randomized field trials).
-  metrics::MetricsService* metrics = application_context_->GetMetricsService();
-
   // Initialize FieldTrialList to support FieldTrials that use one-time
   // randomization.
+  DCHECK(!field_trial_list_);
   field_trial_list_.reset(
-      new base::FieldTrialList(metrics->CreateEntropyProvider().release()));
+      new base::FieldTrialList(application_context_->GetMetricsServicesManager()
+                                   ->CreateEntropyProvider()
+                                   .release()));
 
   const base::CommandLine* command_line =
       base::CommandLine::ForCurrentProcess();
@@ -228,6 +226,11 @@ void IOSChromeMainParts::SetUpMetricsAndFieldTrials() {
   std::vector<std::string> variation_ids =
       RegisterAllFeatureVariationParameters(&flags_storage, feature_list.get());
 
+  // Must initialize metrics after about:flags have been converted into
+  // switches, but before field trials are set up (so that client ID is
+  // available for one-time randomized field trials).
+  metrics::MetricsService* metrics = application_context_->GetMetricsService();
+
   variations::VariationsHttpHeaderProvider* http_header_provider =
       variations::VariationsHttpHeaderProvider::GetInstance();
   // Force the variation ids selected in chrome://flags and/or specified using

ios/chrome/browser/metrics/ios_chrome_metrics_services_manager_client.h

@@ -8,6 +8,7 @@
 #include <memory>
 
 #include "base/macros.h"
+#include "base/metrics/field_trial.h"
 #include "base/threading/thread_checker.h"
 #include "components/metrics_services_manager/metrics_services_manager_client.h"
 
@@ -38,6 +39,9 @@ class IOSChromeMetricsServicesManagerClient
       override;
   std::unique_ptr<metrics::MetricsServiceClient> CreateMetricsServiceClient()
       override;
+  std::unique_ptr<const base::FieldTrial::EntropyProvider>
+  CreateEntropyProvider() override;
+
   net::URLRequestContextGetter* GetURLRequestContext() override;
   bool IsSafeBrowsingEnabled(const base::Closure& on_update_callback) override;
   bool IsMetricsReportingEnabled() override;

ios/chrome/browser/metrics/ios_chrome_metrics_services_manager_client.mm

@@ -80,6 +80,11 @@ IOSChromeMetricsServicesManagerClient::CreateMetricsServiceClient() {
   return IOSChromeMetricsServiceClient::Create(GetMetricsStateManager());
 }
 
+std::unique_ptr<const base::FieldTrial::EntropyProvider>
+IOSChromeMetricsServicesManagerClient::CreateEntropyProvider() {
+  return GetMetricsStateManager()->CreateDefaultEntropyProvider();
+}
+
 net::URLRequestContextGetter*
 IOSChromeMetricsServicesManagerClient::GetURLRequestContext() {
   return GetApplicationContext()->GetSystemURLRequestContext();