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
  RelayFlush(base::PlatformFile file,
             base::FileUtilProxy::StatusCallback* callback)
      : RelayWithStatusCallback(callback),
        file_(file) {
  }

  RelayFlush(base::PlatformFile file,
             base::FileUtilProxy::StatusCallback* callback)
      : RelayWithStatusCallback(callback),
        file_(file) {
  }
