Null check frame in Document::dispatchDisabledAdaptationsDidChangeForMainFrame and...

Null check frame in Document::dispatchDisabledAdaptationsDidChangeForMainFrame and a few other places
https://bugs.webkit.org/show_bug.cgi?id=214715
<rdar://problem/65467702>

Reviewed by Geoffrey Garen.

Source/WebCore:

Test: security/mutation-observer-frame-detach.html

* dom/Document.cpp:
(WebCore::Document::didBecomeCurrentDocumentInFrame):
(WebCore::Document::initContentSecurityPolicy):
* loader/DocumentLoader.cpp:
(WebCore::DocumentLoader::commitData):
Add some null checks and early returns if the frame detaches.
* loader/SubframeLoader.cpp:
(WebCore::FrameLoader::SubframeLoader::loadSubframe):
Balance the call to incrementLoadEventDelayCount in the early return case or this test never finishes loading.

LayoutTests:

* security/mutation-observer-frame-detach-expected.txt: Added.
* security/mutation-observer-frame-detach.html: Added.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@264880 268f45cc-cd09-0410-ab3c-d52691b4dbfc