Make FileReader return ownership of the string content

extensions/browser/file_reader_unittest.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/bind.h"
 #include "base/bind_helpers.h"
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/message_loop/message_loop.h"
 #include "base/path_service.h"
@@ skipping 22 matching lines @@
 class Receiver {
  public:
   Receiver() : succeeded_(false) {
   }
 
   FileReader::Callback NewCallback() {
     return base::Bind(&Receiver::DidReadFile, base::Unretained(this));
   }
 
   bool succeeded() const { return succeeded_; }
-  const std::string& data() const { return data_; }
+  const std::string& data() const { return *data_; }
 
  private:
-  void DidReadFile(bool success, const std::string& data) {
+  void DidReadFile(bool success, std::unique_ptr<std::string> data) {
     succeeded_ = success;
-    data_ = data;
+    data_ = std::move(data);
     base::MessageLoop::current()->QuitWhenIdle();
   }
 
   bool succeeded_;
-  std::string data_;
+  std::unique_ptr<std::string> data_;
 };
 
 void RunBasicTest(const char* filename) {
   base::FilePath path;
   PathService::Get(DIR_TEST_DATA, &path);
   std::string extension_id = crx_file::id_util::GenerateId("test");
   ExtensionResource resource(
       extension_id, path, base::FilePath().AppendASCII(filename));
   path = path.AppendASCII(filename);
 
@@ skipping 33 matching lines @@
   scoped_refptr<FileReader> file_reader(
       new FileReader(resource, receiver.NewCallback()));
   file_reader->Start();
 
   base::RunLoop().Run();
 
   EXPECT_FALSE(receiver.succeeded());
 }
 
 }  // namespace extensions