seamless iframes don't inherit styles when srcdoc is used
https://bugs.webkit.org/show_bug.cgi?id=103539

Reviewed by Antti Koivisto.

Source/WebCore:

Seamless iframes populated via a 'srcdoc' attribute should always
inherit styles from their parent documents. At the moment, this is
only the case when they contain a stylesheet or some other markup
that forces a style recalculation on the document. Simple 'srcdoc'
attributes (e.g. "srcdoc='<p>This is a comment.</p>'") bail out of
recalculating style early, resulting in unstyled appearance.

This patch instructs WebCore to treat seamless documents as having an
updated StyleResolver regardless of what actions the parser takes,
which in turn ensures that the document's style is recalculated
correctly.

Test: fast/frames/seamless/seamless-srcdoc.html

* dom/Document.cpp:
(WebCore::Document::implicitOpen):
    If it's a seamless document, notify it that its StyleResolver isn't
    what it might have expected.

LayoutTests:

* fast/frames/seamless/resources/span.html: Added.
* fast/frames/seamless/seamless-contenteditable-not-inherited-expected.txt:
    Updating the previously failing expectation.
* fast/frames/seamless/seamless-srcdoc-expected.txt: Added.
* fast/frames/seamless/seamless-srcdoc.html: Added.
    Exciting new test to ensure that this doesn't regress, neither
    for totally simple srcdoc attriubtes, nor for slightly more
    complex variations.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@138704 268f45cc-cd09-0410-ab3c-d52691b4dbfc