Make base:ReplaceFile return an informative error.

base/platform_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_PLATFORM_FILE_H_
 #define BASE_PLATFORM_FILE_H_
 
 #include "build/build_config.h"
 #if defined(OS_WIN)
 #include <windows.h>
@@ skipping 186 matching lines @@
 BASE_EXPORT bool FlushPlatformFile(PlatformFile file);
 
 // Touches the given file.
 BASE_EXPORT bool TouchPlatformFile(PlatformFile file,
                                    const Time& last_access_time,
                                    const Time& last_modified_time);
 
 // Returns some information for the given file.
 BASE_EXPORT bool GetPlatformFileInfo(PlatformFile file, PlatformFileInfo* info);
 
+#if defined(OS_WIN)
+PlatformFileError LastErrorToPlatformFileError(DWORD saved_errno);
+#elif defined(OS_POSIX)
+PlatformFileError ErrnoToPlatformFileError(int saved_errno);
+#endif
+
 // Use this class to pass ownership of a PlatformFile to a receiver that may or
 // may not want to accept it.  This class does not own the storage for the
 // PlatformFile.
 //
 // EXAMPLE:
 //
 //  void MaybeProcessFile(PassPlatformFile pass_file) {
 //    if (...) {
 //      PlatformFile file = pass_file.ReleaseValue();
 //      // Now, we are responsible for closing |file|.
@@ skipping 21 matching lines @@
     return temp;
   }
 
  private:
   PlatformFile* value_;
 };
 
 }  // namespace base
 
 #endif  // BASE_PLATFORM_FILE_H_