configure.ac has duplicated AC_MSG_RESULT([$enable_sandbox]) and nothing for seamless iframes
https://bugs.webkit.org/show_bug.cgi?id=87453

Reviewed by Eric Seidel.

Report the value of $enable_iframe_seamless rather than $enable_sandbox
after checking whether to enable the iframe seamless option.

* configure.ac:


git-svn-id: svn://svn.chromium.org/blink/trunk@118550 bbb929c8-8fbe-4397-9dbb-9b2b20218538