[chromecast] ExternalMetrics has to destroy itself in file thread.

chromecast/browser/metrics/external_metrics.cc

 // 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.
 
 #include "chromecast/browser/metrics/external_metrics.h"
 
 #include <string>
 
 #include "base/bind.h"
 #include "base/files/file_path.h"
@@ skipping 40 matching lines @@
 const char kEventsFilePath[] = "/data/share/chrome/metrics/uma-events";
 
 ExternalMetrics::ExternalMetrics(
     CastStabilityMetricsProvider* stability_provider)
     : stability_provider_(stability_provider),
       uma_events_file_(kEventsFilePath),
       weak_factory_(this) {
   DCHECK(stability_provider);
 }
 
-ExternalMetrics::~ExternalMetrics() {}
+ExternalMetrics::~ExternalMetrics() {
+}
+
+void ExternalMetrics::StopAndDestroy() {
+  content::BrowserThread::DeleteSoon(
+      content::BrowserThread::FILE, FROM_HERE, this);
+}
 
 void ExternalMetrics::Start() {
   ScheduleCollector();
 }
 
 void ExternalMetrics::RecordCrash(const std::string& crash_kind) {
   content::BrowserThread::PostTask(
       content::BrowserThread::UI, FROM_HERE,
       base::Bind(&CastStabilityMetricsProvider::LogExternalCrash,
                  base::Unretained(stability_provider_),
@@ skipping 64 matching lines @@
       content::BrowserThread::FILE,
       FROM_HERE,
       base::Bind(&ExternalMetrics::CollectEventsAndReschedule,
                  weak_factory_.GetWeakPtr()),
       base::TimeDelta::FromSeconds(kExternalMetricsCollectionIntervalSeconds));
   DCHECK(result);
 }
 
 }  // namespace metrics
 }  // namespace chromecast