Only support AddFeatures invalidation set mode for :host or
:any in selector components to the right of the rightmost
descendant relation.

This fixes a bug that caused this to be the case accidentally in cases such as:

:host(.foo) #bar

when #bar is not (yet) supported for the style invalidation
tree walk.

BUG=358704

Review URL: https://codereview.chromium.org/221643002

git-svn-id: svn://svn.chromium.org/blink/trunk@170637 bbb929c8-8fbe-4397-9dbb-9b2b20218538