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

base/files/file_unittest.cc

Index: base/files/file_unittest.cc
diff --git a/base/files/file_unittest.cc b/base/files/file_unittest.cc
index 66c312b60d4cff0d296384d829e529db94a74d28..8275bac769c04f133fce7a182e36bb0686560b08 100644
--- a/base/files/file_unittest.cc
+++ b/base/files/file_unittest.cc
@@ -105,6 +105,16 @@ TEST(FileTest, Create) {
   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());