Prefer ScopedNestableTaskAllower over manual save/restore

net/base/file_stream_unittest.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 "net/base/file_stream.h"
 
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/file_util.h"
 #include "base/message_loop.h"
@@ skipping 731 matching lines @@
       *total_bytes_read_ += total_bytes_read;
       *data_read_ += data_read;
     } else {  // We're done writing all data.  Start reading the data.
       stream_->Seek(FROM_BEGIN, 0);
 
       TestCompletionCallback callback;
       for (;;) {
         char buf[4];
         rv = stream_->Read(buf, arraysize(buf), callback.callback());
         if (rv == ERR_IO_PENDING) {
-          bool old_state = MessageLoop::current()->NestableTasksAllowed();
-          MessageLoop::current()->SetNestableTasksAllowed(true);
+          MessageLoop::ScopedNestableTaskAllower allow(MessageLoop::current());
           rv = callback.WaitForResult();
-          MessageLoop::current()->SetNestableTasksAllowed(old_state);
         }
         EXPECT_LE(0, rv);
         if (rv <= 0)
           break;
         *total_bytes_read_ += rv;
         data_read_->append(buf, rv);
       }
     }
 
     result_ = *total_bytes_written_;
@@ skipping 176 matching lines @@
   // Read in the contents and make sure we get back what we expected.
   std::string read_contents;
   EXPECT_TRUE(file_util::ReadFileToString(temp_file_path(), &read_contents));
 
   EXPECT_EQ("01230123", read_contents);
 }
 
 }  // namespace
 
 }  // namespace net