Update from https://crrev.com/328418

base/files/important_file_writer.cc

 // Copyright (c) 2011 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 "base/files/important_file_writer.h"
 
 #include <stdio.h>
 
 #include <string>
 
@@ skipping 33 matching lines @@
 };
 
 void LogFailure(const FilePath& path, TempFileFailure failure_code,
                 const std::string& message) {
   UMA_HISTOGRAM_ENUMERATION("ImportantFile.TempFileFailures", failure_code,
                             TEMP_FILE_FAILURE_MAX);
   DPLOG(WARNING) << "temp file failure: " << path.value().c_str()
                  << " : " << message;
 }
 
+// Helper function to call WriteFileAtomically() with a scoped_ptr<std::string>.
+bool WriteScopedStringToFileAtomically(const FilePath& path,
+                                       scoped_ptr<std::string> data) {
+  return ImportantFileWriter::WriteFileAtomically(path, *data);
+}
+
 }  // namespace
 
 // static
 bool ImportantFileWriter::WriteFileAtomically(const FilePath& path,
                                               const std::string& data) {
 #if defined(OS_CHROMEOS)
   // On Chrome OS, chrome gets killed when it cannot finish shutdown quickly,
   // and this function seems to be one of the slowest shutdown steps.
   // Include some info to the report for investigation. crbug.com/418627
   // TODO(hashimoto): Remove this.
@@ skipping 53 matching lines @@
 
 ImportantFileWriter::ImportantFileWriter(
     const FilePath& path,
     const scoped_refptr<base::SequencedTaskRunner>& task_runner)
     : path_(path),
       task_runner_(task_runner),
       serializer_(NULL),
       commit_interval_(TimeDelta::FromMilliseconds(kDefaultCommitIntervalMs)),
       weak_factory_(this) {
   DCHECK(CalledOnValidThread());
-  DCHECK(task_runner_.get());
+  DCHECK(task_runner_);
 }
 
 ImportantFileWriter::~ImportantFileWriter() {
   // We're usually a member variable of some other object, which also tends
   // to be our serializer. It may not be safe to call back to the parent object
   // being destructed.
   DCHECK(!HasPendingWrite());
 }
 
 bool ImportantFileWriter::HasPendingWrite() const {
   DCHECK(CalledOnValidThread());
   return timer_.IsRunning();
 }
 
-void ImportantFileWriter::WriteNow(const std::string& data) {
+void ImportantFileWriter::WriteNow(scoped_ptr<std::string> data) {
   DCHECK(CalledOnValidThread());
-  if (data.length() > static_cast<size_t>(kint32max)) {
+  if (data->length() > static_cast<size_t>(kint32max)) {
     NOTREACHED();
     return;
   }
 
   if (HasPendingWrite())
     timer_.Stop();
 
-  if (!PostWriteTask(data)) {
+  auto task = Bind(&WriteScopedStringToFileAtomically, path_, Passed(&data));
+  if (!PostWriteTask(task)) {
     // Posting the task to background message loop is not expected
     // to fail, but if it does, avoid losing data and just hit the disk
     // on the current thread.
     NOTREACHED();
 
-    WriteFileAtomically(path_, data);
+    task.Run();
   }
 }
 
 void ImportantFileWriter::ScheduleWrite(DataSerializer* serializer) {
   DCHECK(CalledOnValidThread());
 
   DCHECK(serializer);
   serializer_ = serializer;
 
   if (!timer_.IsRunning()) {
     timer_.Start(FROM_HERE, commit_interval_, this,
                  &ImportantFileWriter::DoScheduledWrite);
   }
 }
 
 void ImportantFileWriter::DoScheduledWrite() {
   DCHECK(serializer_);
-  std::string data;
-  if (serializer_->SerializeData(&data)) {
-    WriteNow(data);
+  scoped_ptr<std::string> data(new std::string);
+  if (serializer_->SerializeData(data.get())) {
+    WriteNow(data.Pass());
   } else {
     DLOG(WARNING) << "failed to serialize data to be saved in "
                   << path_.value().c_str();
   }
   serializer_ = NULL;
 }
 
 void ImportantFileWriter::RegisterOnNextSuccessfulWriteCallback(
     const base::Closure& on_next_successful_write) {
   DCHECK(on_next_successful_write_.is_null());
   on_next_successful_write_ = on_next_successful_write;
 }
 
-bool ImportantFileWriter::PostWriteTask(const std::string& data) {
+bool ImportantFileWriter::PostWriteTask(const Callback<bool()>& task) {
   // TODO(gab): This code could always use PostTaskAndReplyWithResult and let
   // ForwardSuccessfulWrite() no-op if |on_next_successful_write_| is null, but
   // PostTaskAndReply causes memory leaks in tests (crbug.com/371974) and
   // suppressing all of those is unrealistic hence we avoid most of them by
   // using PostTask() in the typical scenario below.
   if (!on_next_successful_write_.is_null()) {
     return base::PostTaskAndReplyWithResult(
         task_runner_.get(),
         FROM_HERE,
-        MakeCriticalClosure(
-            Bind(&ImportantFileWriter::WriteFileAtomically, path_, data)),
+        MakeCriticalClosure(task),
         Bind(&ImportantFileWriter::ForwardSuccessfulWrite,
              weak_factory_.GetWeakPtr()));
   }
   return task_runner_->PostTask(
       FROM_HERE,
-      MakeCriticalClosure(
-          Bind(IgnoreResult(&ImportantFileWriter::WriteFileAtomically),
-               path_, data)));
+      MakeCriticalClosure(base::Bind(IgnoreResult(task))));
 }
 
 void ImportantFileWriter::ForwardSuccessfulWrite(bool result) {
   DCHECK(CalledOnValidThread());
   if (result && !on_next_successful_write_.is_null()) {
     on_next_successful_write_.Run();
     on_next_successful_write_.Reset();
   }
 }
 
 }  // namespace base