When detaching insertion points we should reattach the distribution

When an InsertionPoint is detached we should reattach all the distributed nodes
instead of just detaching them since that would leave detached nodes in the tree
which prevents the distribution process from reattaching them later.

BUG=274676

Review URL: https://chromiumcodereview.appspot.com/22980013

git-svn-id: svn://svn.chromium.org/blink/trunk@156454 bbb929c8-8fbe-4397-9dbb-9b2b20218538