Revert of Either content elements or shadow elements should not be treated as insertion points if they are no… (https://codereview.chromium.org/133213008/)

Reason for revert:
This patch might cause inconsistency between Polyfill and native Shadow DOM. It might be better to revert this patch until we have clear consensus for this change.

Original issue's description:
> Either content elements or shadow elements should not be treated as insertion points if they are not in document.
> 
> The relevant spec update: https://github.com/w3c/webcomponents/commit/69fbceabe01786ba3740728a6b86f5ec958f69b4
> 
> This behavior is similar to that of styles, which are not calculated for disconnected nodes.
> 
> This change also makes it possible to add an assertion, ASSERT(shadowRoot), for rootNode of an insertionPoint in InsertionPoint::isActive.
> 
> BUG=339029
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=166647

TBR=esprehn@google.com,dglazkov@chromium.org,morrita@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=339029

Review URL: https://codereview.chromium.org/156653004

git-svn-id: svn://svn.chromium.org/blink/trunk@166802 bbb929c8-8fbe-4397-9dbb-9b2b20218538