It's confusing to have both DOM and renderer checks in one function.
There are only two callers of Document::isFrameSet():
1. LegacyWebArchive::createFromSelection(). It doesn't seem to depend on render tree at all.
2. FrameLoader::shouldScrollToAnchor(). Returning true from Document::isFrameSet() means that we won't scroll, which seems like a good idea if there's no renderer.
The check has been there since the method was added in <http://trac.webkit.org/changeset/1564>.
Created attachment 72222 [details]