Remove complexity related to m_cachedElementsArrayOffset from LiveNodeListBase

Remove complexity related to m_cachedElementsArrayOffset from LiveNodeListBase
and HTMLCollection. The complexity is moved to HTMLFormControlsCollection
which is the only type that actually needs to cache this offset.

The code in LiveNodeListBase / HTMLCollection is overly complex and this is one
step towards improving the situation.

This change is a partial merge of WebKit r158758 by <antti@apple.com>.

R=abarth, esprehn, eseidel

Review URL: https://codereview.chromium.org/113653006

git-svn-id: svn://svn.chromium.org/blink/trunk@164452 bbb929c8-8fbe-4397-9dbb-9b2b20218538