Move LiveNodeList code out of HTMLCollection.cpp

Move LiveNodeList code out of HTMLCollection.cpp and into the LiveNodeList.*
files. Code that is shared between LiveNodeList and HTMLCollection was moved
to the LiveNodeListBase header.

R=adamk, esprehn

Review URL: https://codereview.chromium.org/181103005

git-svn-id: svn://svn.chromium.org/blink/trunk@167926 bbb929c8-8fbe-4397-9dbb-9b2b20218538