Fix a small leak in FileUtilProxy

BUG=none
TEST=green mem bots

Review URL: http://codereview.chromium.org/7669046

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@97451 0039d316-1c4b-4281-b951-d872f2087c98
  virtual void RunWork() {
    bytes_read_ = base::ReadPlatformFile(file_, offset_, buffer_.get(),
                                         bytes_to_read_);
    if (bytes_read_ < 0)
      set_error_code(base::PLATFORM_FILE_ERROR_FAILED);
  }

  virtual void RunWork() {
    bytes_read_ = base::ReadPlatformFile(file_, offset_, buffer_.get(),
                                         bytes_to_read_);
    if (bytes_read_ < 0)
      set_error_code(base::PLATFORM_FILE_ERROR_FAILED);
  }
