The ownerScope property is equivalent to walking up the parentNode
pointers until you hit the top and returning that node if it's a
Document or ShadowRoot.
This means that the ownerScope of ShadowRoot and Document is always
itself, and the ownerScope of an Element that is not the descendant
of a ShadowRoot, and is not in the document is null.
R=eseidel@chromium.org
Review URL: https://codereview.chromium.org/810793005
We can simplify the checks given that there's fewer node types now. This does
make the error messages from Range a little worse, but it's weird that Range
is doing its own error checking anyway.
I also took this as an opportunity to add a bunch of DOM tests.
R=ojan@chromium.org
Review URL: https://codereview.chromium.org/732203004
