[Cleanup] Migrate ExternalMetrics to use the Task Scheduler.

chromecast/browser/metrics/external_metrics.h

 // Copyright 2014 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 CHROMECAST_BROWSER_METRICS_EXTERNAL_METRICS_H_
 #define CHROMECAST_BROWSER_METRICS_EXTERNAL_METRICS_H_
 
 #include <string>
 
 #include "base/callback_forward.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
+#include "base/sequence_checker.h"
 #include "base/sequenced_task_runner_helpers.h"
 
 namespace metrics {
 class MetricSample;
 }  // namespace metrics
 
 namespace chromecast {
 namespace metrics {
 
 class CastStabilityMetricsProvider;
@@ skipping 32 matching lines @@
 
   // Collects external events from metrics log file.  This is run at periodic
   // intervals.
   //
   // Returns the number of events collected.
   int CollectEvents();
 
   // Calls CollectEvents and reschedules a future collection.
   void CollectEventsAndReschedule();
 
+  // Schedules a future collection.
+  void ScheduleCollection();
+
   // Reference to stability metrics provider, for reporting external crashes.
   CastStabilityMetricsProvider* const stability_provider_;
 
   // File used by libmetrics to send metrics to the browser process.
   const std::string uma_events_file_;
 
+  // The task runner used for running background tasks.
+  scoped_refptr<base::SequencedTaskRunner> task_runner_;
+
+  SEQUENCE_CHECKER(sequence_checker_);
+
   base::WeakPtrFactory<ExternalMetrics> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ExternalMetrics);
 };
 
 }  // namespace metrics
 }  // namespace chromecast
 
 #endif  // CHROMECAST_BROWSER_METRICS_EXTERNAL_METRICS_H_