Base: Don't check for thread restrictions when closing a file doesn't do IO.

base/files/file.h

 // 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.
 
 #ifndef BASE_FILES_FILE_H_
 #define BASE_FILES_FILE_H_
 
 #include "build/build_config.h"
 #if defined(OS_WIN)
 #include <windows.h>
@@ skipping 153 matching lines @@
   // components. Use only with extreme care.
   void InitializeUnsafe(const FilePath& name, uint32 flags);
 
   bool IsValid() const;
 
   // Returns true if a new file was created (or an old one truncated to zero
   // length to simulate a new file, which can happen with
   // FLAG_CREATE_ALWAYS), and false otherwise.
   bool created() const { return created_; }
 
-  // Returns the OS result of opening this file.
+  // Returns the OS result of opening this file. Note that the way to verify
+  // the success of the operation is to use IsValid(), not this method:
+  //   File file(name, flags);
+  //   if (!file.IsValid())
+  //     return;
   Error error_details() const { return error_details_; }
 
   PlatformFile GetPlatformFile() const { return file_; }
   PlatformFile TakePlatformFile();
 
   // Destroying this object closes the file automatically.
   void Close();
 
   // Changes current position in the file to an |offset| relative to an origin
   // defined by |whence|. Returns the resultant current position in the file
@@ skipping 92 matching lines @@
 #endif
 
   Error error_details_;
   bool created_;
   bool async_;
 };
 
 }  // namespace base
 
 #endif  // BASE_FILES_FILE_H_