Move the thread hop for UMA user actions from content:: to base::.

ios/chrome/browser/metrics/mobile_session_shutdown_metrics_provider_unittest.mm

 // Copyright 2015 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/metrics/mobile_session_shutdown_metrics_provider.h"
 
 #include <memory>
 
 #include "base/bind.h"
 #include "base/macros.h"
+#include "base/metrics/user_metrics.h"
 #include "base/test/histogram_tester.h"
 #include "components/metrics/metrics_pref_names.h"
 #include "components/metrics/metrics_service.h"
 #include "components/metrics/metrics_state_manager.h"
 #include "components/metrics/test_metrics_service_client.h"
 #include "components/prefs/testing_pref_service.h"
 #include "testing/gtest/include/gtest/gtest-param-test.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace {
@@ skipping 124 matching lines @@
       FIRST_LAUNCH_AFTER_UPGRADE,
   };
 
   // Setup the MetricsService.
   local_state_.SetBoolean(metrics::prefs::kStabilityExitedCleanly,
                           was_last_shutdown_clean);
   metrics_state_ = metrics::MetricsStateManager::Create(
       &local_state_, base::Bind(&IsMetricsReportingEnabled),
       metrics::MetricsStateManager::StoreClientInfoCallback(),
       metrics::MetricsStateManager::LoadClientInfoCallback());
+  base::ResetRecordActionTaskRunnerForTesting();
   metrics_service_.reset(new metrics::MetricsService(
       metrics_state_.get(), &metrics_client_, &local_state_));
 
   // Create the metrics provider to test.
   metrics_provider_.reset(new MobileSessionShutdownMetricsProviderForTesting(
       metrics_service_.get()));
 
   // Setup the metrics provider for the current test.
   metrics_provider_->set_is_first_launch_after_upgrade(
       is_first_launch_after_upgrade);
@@ skipping 10 matching lines @@
   // Now call the method under test and verify exactly one sample is written to
   // the expected bucket.
   metrics_provider_->ProvideInitialStabilityMetrics(nullptr);
   histogram_tester.ExpectUniqueSample("Stability.MobileSessionShutdownType",
                                       expected_buckets[GetParam()], 1);
 }
 
 INSTANTIATE_TEST_CASE_P(/* No InstantiationName */,
                         MobileSessionShutdownMetricsProviderTest,
                         testing::Range(0, 32));