Reviewed by Simon Fraser.

        Made composited iframes work on Windows
        https://bugs.webkit.org/show_bug.cgi?id=32446

        I've added one new test (composited-parent-iframe.html) which
        shows both the parent iframe and the iframe contents document
        with compositing. It also shows correct behavior with clipping,
        borders, margins, padding and shadows. It also sets the iframe
        size as a percent of the page to show correct resizing behavior.
        The existing composited-iframe.html has been changed similarly
        but without the page resizing. The existing preserve-3d-switching.html
        test needed new results because of changes to the layer dumper.

        * compositing/geometry/preserve-3d-switching-expected.txt:
        * compositing/iframes/composited-iframe.html:
        * compositing/iframes/composited-parent-iframe.html: Added.
        * compositing/iframes/resources/composited-subframe.html:
        * platform/win/compositing/iframes/composited-iframe-expected.txt:
        * platform/win/compositing/iframes/composited-parent-iframe-expected.txt: Added.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@58798 268f45cc-cd09-0410-ab3c-d52691b4dbfc