Don't force recalc if there are no shadow boundary crossing rules

Review URL: https://codereview.chromium.org/119693002

git-svn-id: svn://svn.chromium.org/blink/trunk@164382 bbb929c8-8fbe-4397-9dbb-9b2b20218538
HTMLCollection should not inherit NodeList

HTMLCollection should not inherit NodeList. Those types are unrelated in DOM so
having one inherit the other on native side was confusing. It also led to:
- HTMLCollection redefining isLiveNodeList() which was virtual in NodeList
- HTMLCollection::item() / HTMLCollection::length() were needlessly virtual,
  which is bad for performance

R=abarth, esprehn

Review URL: https://codereview.chromium.org/120383002

git-svn-id: svn://svn.chromium.org/blink/trunk@164383 bbb929c8-8fbe-4397-9dbb-9b2b20218538