Fix issue with previousElementSibling
Move olderShadowRoot to ShadowRoot
Merge pull request #184 from arv/previous-element-sibling

Fix issue with previousElementSibling
Merge pull request #185 from arv/older-shadow-root-should-be-on-shadow-root

Move olderShadowRoot to ShadowRoot
Merge pull request #192 from Polymer/master

8/1 master -> stable