Revert of Add a default task runner argument to the constructor of JsonPrefStore.

components/prefs/json_pref_store.cc

 // Copyright (c) 2012 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 "components/prefs/json_pref_store.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <utility>
@@ skipping 125 matching lines @@
     base::SequencedWorkerPool* worker_pool) {
   std::string token("json_pref_store-");
   token.append(filename.AsUTF8Unsafe());
   return worker_pool->GetSequencedTaskRunnerWithShutdownBehavior(
       worker_pool->GetNamedSequenceToken(token),
       base::SequencedWorkerPool::BLOCK_SHUTDOWN);
 }
 
 JsonPrefStore::JsonPrefStore(
     const base::FilePath& pref_filename,
-    scoped_refptr<base::SequencedTaskRunner> sequenced_task_runner,
+    const scoped_refptr<base::SequencedTaskRunner>& sequenced_task_runner,
     std::unique_ptr<PrefFilter> pref_filter)
     : path_(pref_filename),
-      sequenced_task_runner_(std::move(sequenced_task_runner)),
+      sequenced_task_runner_(sequenced_task_runner),
       prefs_(new base::DictionaryValue()),
       read_only_(false),
-      writer_(pref_filename, sequenced_task_runner_),
+      writer_(pref_filename, sequenced_task_runner),
       pref_filter_(std::move(pref_filter)),
       initialized_(false),
       filtering_in_progress_(false),
       pending_lossy_write_(false),
       read_error_(PREF_READ_ERROR_NONE),
       has_pending_write_reply_(false),
       write_count_histogram_(writer_.commit_interval(), path_) {
   DCHECK(!path_.empty());
 }
 
@@ skipping 422 matching lines @@
   DCHECK_EQ(31, num_buckets);
 
   // The histogram below is an expansion of the UMA_HISTOGRAM_CUSTOM_COUNTS
   // macro adapted to allow for a dynamically suffixed histogram name.
   // Note: The factory creates and owns the histogram.
   base::HistogramBase* histogram = base::Histogram::FactoryGet(
       histogram_name, min_value, max_value, num_buckets,
       base::HistogramBase::kUmaTargetedHistogramFlag);
   return histogram;
 }