Add other variations (with ids) for NTPSnippets to chrome://flags

ios/chrome/browser/ios_chrome_main_parts.mm

 // Copyright 2016 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 "ios/chrome/browser/ios_chrome_main_parts.h"
 
 #include "base/base_switches.h"
 #include "base/feature_list.h"
 #include "base/files/file_path.h"
 #include "base/logging.h"
@@ skipping 82 matching lines @@
   // Check the first run state early; this must be done before IO is disallowed
   // so that later calls can use the cached value. (The return value is ignored
   // because this is only to trigger the internal lookup and caching for later
   // use.)
   FirstRun::IsChromeFirstRun();
 
   // Initialize local state.
   local_state_ = application_context_->GetLocalState();
   DCHECK(local_state_);
 
-  flags_ui::PrefServiceFlagsStorage flags_storage_(
+  flags_ui::PrefServiceFlagsStorage flags_storage(
       application_context_->GetLocalState());
-  ConvertFlagsToSwitches(&flags_storage_,
+  ConvertFlagsToSwitches(&flags_storage,
                          base::CommandLine::ForCurrentProcess());
 
   // Initialize tracking synchronizer system.
   tracking_synchronizer_ = new metrics::TrackingSynchronizer(
       base::WrapUnique(new base::DefaultTickClock()),
       base::Bind(&metrics::IOSTrackingSynchronizerDelegate::Create));
 
   // Now the command line has been mutated based on about:flags, we can setup
   // metrics and initialize field trials that are needed by IOSChromeIOThread's
   // initialization which happens in ApplicationContext:PreCreateThreads.
@@ skipping 93 matching lines @@
   // Also stop the metrics service so that we don't pollute UMA.
   if (command_line->HasSwitch(switches::kForceFieldTrials)) {
     // Create field trials without activating them, so that this behaves in a
     // consistent manner with field trials created from the server.
     bool result = base::FieldTrialList::CreateTrialsFromString(
         command_line->GetSwitchValueASCII(switches::kForceFieldTrials),
         std::set<std::string>());
     CHECK(result) << "Invalid --" << switches::kForceFieldTrials
                   << " list specified.";
   }
-  if (command_line->HasSwitch(switches::kIOSForceVariationIds)) {
-    // Create default variation ids which will always be included in the
-    // X-Client-Data request header.
-    variations::VariationsHttpHeaderProvider* provider =
-        variations::VariationsHttpHeaderProvider::GetInstance();
-    bool result = provider->SetDefaultVariationIds(
-        command_line->GetSwitchValueASCII(switches::kIOSForceVariationIds));
-    CHECK(result) << "Invalid --" << switches::kIOSForceVariationIds
-                  << " list specified.";
-  }
+
   std::unique_ptr<base::FeatureList> feature_list(new base::FeatureList);
+
+  // Associate parameters chosen in about:flags and create trial/group for them.
+  flags_ui::PrefServiceFlagsStorage flags_storage(
+      application_context_->GetLocalState());
+  std::vector<std::string> variation_ids =
+      RegisterAllFeatureVariationParameters(&flags_storage, feature_list.get());
+
+  variations::VariationsHttpHeaderProvider* http_header_provider =
+      variations::VariationsHttpHeaderProvider::GetInstance();
+  // Force the variation ids selected in chrome://flags and/or specified using
+  // the command-line flag.
+  bool result = http_header_provider->ForceVariationIds(
+      command_line->GetSwitchValueASCII(switches::kIOSForceVariationIds),
+      &variation_ids);
+  CHECK(result) << "Invalid list of variation ids specified (either in --"
+                << switches::kIOSForceVariationIds << " or in chrome://flags)";
+  metrics->AddSyntheticTrialObserver(http_header_provider);
+
   feature_list->InitializeFromCommandLine(
       command_line->GetSwitchValueASCII(switches::kEnableIOSFeatures),
       command_line->GetSwitchValueASCII(switches::kDisableIOSFeatures));
 
   variations::VariationsService* variations_service =
       application_context_->GetVariationsService();
   if (variations_service)
     variations_service->CreateTrialsFromSeed(feature_list.get());
 
   base::FeatureList::SetInstance(std::move(feature_list));
 
   SetupFieldTrials(parsed_command_line_,
                    base::Time::FromTimeT(metrics->GetInstallDate()));
 
   // Now that field trials have been created, initializes metrics recording.
   metrics->InitializeMetricsRecordingState();
 }
 
 void IOSChromeMainParts::StartMetricsRecording() {
   bool wifiOnly = local_state_->GetBoolean(prefs::kMetricsReportingWifiOnly);
   bool isConnectionCellular = net::NetworkChangeNotifier::IsConnectionCellular(
       net::NetworkChangeNotifier::GetConnectionType());
   bool mayUpload = !wifiOnly || !isConnectionCellular;
 
   application_context_->GetMetricsServicesManager()->UpdateUploadPermissions(
       mayUpload);
 }