Don't use cached inherited props for distributed nodes.

The -webkit-user-modify, which is inherited, does not follow normal inheritance
for distributed nodes in a shadow dom tree. Distributed nodes will have
-webkit-user-modify propagated from the shadow host overriding any inheritance
from non-distributed shadow dom nodes.

This propagation, which happens in StyleResolver::styleForElement will not be
caught will not be caught when computing the cacheHash in
StyleResolver::applyMatchedProperties and the inherited properties might
incorrectly be shared, effectively cancelling out the -webkit-user-modify
propagation.

R=esprehn
BUG=339463

Review URL: https://codereview.chromium.org/144853004

git-svn-id: svn://svn.chromium.org/blink/trunk@166414 bbb929c8-8fbe-4397-9dbb-9b2b20218538