Use XFixes to update the clipboard sequence number.

BUG=73478
TEST=manual testing

Review URL: http://codereview.chromium.org/8501002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@109528 0039d316-1c4b-4281-b951-d872f2087c98
bool Clipboard::IsFormatAvailableByString(const std::string& format,
                                          Clipboard::Buffer buffer) const {
  return IsFormatAvailable(format, buffer);
}

bool Clipboard::IsFormatAvailableByString(const std::string& format,
                                          Clipboard::Buffer buffer) const {
  return IsFormatAvailable(format, buffer);
}
