[Cleanup] Migrate the DriveMetricsProvider to use the Task Scheduler.

components/metrics/drive_metrics_provider.h

 // 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.
 
 #ifndef COMPONENTS_METRICS_DRIVE_METRICS_PROVIDER_H_
 #define COMPONENTS_METRICS_DRIVE_METRICS_PROVIDER_H_
 
 #include "base/callback_forward.h"
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
-#include "base/sequenced_task_runner.h"
-#include "base/threading/thread_checker.h"
+#include "base/sequence_checker.h"
 #include "components/metrics/metrics_provider.h"
 #include "components/metrics/proto/system_profile.pb.h"
 
 namespace base {
 class FilePath;
 }
 
 namespace metrics {
 
 // Provides metrics about the local drives on a user's computer. Currently only
 // checks to see if they incur a seek-time penalty (e.g. if they're SSDs).
-//
-// Defers gathering metrics until after "rush hour" (startup) so as to not bog
-// down the file thread.
 class DriveMetricsProvider : public metrics::MetricsProvider {
  public:
-  DriveMetricsProvider(scoped_refptr<base::SequencedTaskRunner> file_thread,
-                       int local_state_path_key);
+  explicit DriveMetricsProvider(int local_state_path_key);
   ~DriveMetricsProvider() override;
 
   // metrics::MetricsDataProvider:
   void ProvideSystemProfileMetrics(
       metrics::SystemProfileProto* system_profile_proto) override;
 
   // Called to start gathering metrics.
   void GetDriveMetrics(const base::Closure& done_callback);
 
  private:
@@ skipping 10 matching lines @@
   struct DriveMetrics {
     SeekPenaltyResponse app_drive;
     SeekPenaltyResponse user_data_drive;
   };
 
   // Determine whether the device that services |path| has a seek penalty.
   // Returns false if it couldn't be determined (e.g., |path| doesn't exist).
   static bool HasSeekPenalty(const base::FilePath& path,
                              bool* has_seek_penalty);
 
-  // Gather metrics about various drives on |file_thread_|.
-  static DriveMetrics GetDriveMetricsOnFileThread(int local_state_path_key);
+  // Gather metrics about various drives. Should be run on a background thread.
+  static DriveMetrics GetDriveMetricsOnBackgroundThread(
+      int local_state_path_key);
 
   // Tries to determine whether there is a penalty for seeking on the drive that
   // hosts |path_service_key| (for example: the drive that holds "Local State").
   static void QuerySeekPenalty(int path_service_key,
                                SeekPenaltyResponse* response);
 
-  // Called when metrics are done being gathered from the FILE thread.
+  // Called when metrics are done being gathered asynchronously.
   // |done_callback| is the callback that should be called once all metrics are
   // gathered.
   void GotDriveMetrics(const base::Closure& done_callback,
                        const DriveMetrics& metrics);
 
   // Fills |drive| with information from successful |response|s.
   void FillDriveMetrics(const SeekPenaltyResponse& response,
                         metrics::SystemProfileProto::Hardware::Drive* drive);
 
-  // The thread on which file operations are performed (supplied by the
-  // embedder).
-  scoped_refptr<base::SequencedTaskRunner> file_thread_;
-
   // The key to give to base::PathService to obtain the path to local state
   // (supplied by the embedder).
   int local_state_path_key_;
 
   // Information gathered about various important drives.
   DriveMetrics metrics_;
 
-  base::ThreadChecker thread_checker_;
+  SEQUENCE_CHECKER(sequence_checker_);
   base::WeakPtrFactory<DriveMetricsProvider> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(DriveMetricsProvider);
 };
 
 }  // namespace metrics
 
 #endif  // COMPONENTS_METRICS_DRIVE_METRICS_PROVIDER_H_