Enable seamless iFrames for Windows DRT.
https://bugs.webkit.org/show_bug.cgi?id=106468.

Rubberstamped by Timothy Horton.

* DumpRenderTree/win/DumpRenderTree.cpp:
(resetDefaultsToConsistentValues):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@139243 268f45cc-cd09-0410-ab3c-d52691b4dbfc