Add a test to ensure that content written into a seamless IFrame inherits style.
https://bugs.webkit.org/show_bug.cgi?id=99289

Reviewed by Eric Seidel.

This patch adds a single test to ensure that content written into a
seamless IFrame via 'contentDocument.write()' properly inherits style.
The root of the issue was fixed in wkbug.com/103539, so no code changes
are necesary, but that patch didn't test this particular edge case.

* fast/frames/seamless/seamless-document-write-expected.txt: Added.
* fast/frames/seamless/seamless-document-write.html: Added.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@140346 268f45cc-cd09-0410-ab3c-d52691b4dbfc