Fixing std::swap(x, x) in base.

base/files/file_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 "base/files/file.h"
 
 #include <stdint.h>
 
 #include <utility>
 
@@ skipping 87 matching lines @@
               base::File::FLAG_OPEN_ALWAYS | base::File::FLAG_READ |
                   base::File::FLAG_DELETE_ON_CLOSE);
     EXPECT_TRUE(file.IsValid());
     EXPECT_TRUE(file.created());
     EXPECT_EQ(base::File::FILE_OK, file.error_details());
   }
 
   EXPECT_FALSE(base::PathExists(file_path));
 }
 
+TEST(FileTest, SelfSwap) {
+  base::ScopedTempDir temp_dir;
+  ASSERT_TRUE(temp_dir.CreateUniqueTempDir());
+  FilePath file_path = temp_dir.GetPath().AppendASCII("create_file_1");
+  File file(file_path,
+            base::File::FLAG_OPEN_ALWAYS | base::File::FLAG_DELETE_ON_CLOSE);
+  std::swap(file, file);
+  EXPECT_TRUE(file.IsValid());
+}
+
 TEST(FileTest, Async) {
   base::ScopedTempDir temp_dir;
   ASSERT_TRUE(temp_dir.CreateUniqueTempDir());
   FilePath file_path = temp_dir.GetPath().AppendASCII("create_file");
 
   {
     File file(file_path, base::File::FLAG_OPEN_ALWAYS | base::File::FLAG_ASYNC);
     EXPECT_TRUE(file.IsValid());
     EXPECT_TRUE(file.async());
   }
@@ skipping 548 matching lines @@
     ASSERT_TRUE(mapping.Initialize(file.Duplicate()));
     ASSERT_EQ(5U, mapping.length());
 
     EXPECT_FALSE(file.DeleteOnClose(true));
   }
 
   file.Close();
   ASSERT_TRUE(base::PathExists(file_path));
 }
 #endif  // defined(OS_WIN)