Merge lazyReattach into lazyReattachIfAttached

No one should be calling lazyReattach() on elements outside the active
document and all elements inside the active document are attached so
it doesn't make sense to have the non IfAttached version of this
function.

Review URL: https://codereview.chromium.org/49153010

git-svn-id: svn://svn.chromium.org/blink/trunk@160790 bbb929c8-8fbe-4397-9dbb-9b2b20218538
FullScreenElementStack should not use confusingAndOftenMisusedAttached()

This code wants Document::isActive() instead.

Review URL: https://codereview.chromium.org/49663003

git-svn-id: svn://svn.chromium.org/blink/trunk@160791 bbb929c8-8fbe-4397-9dbb-9b2b20218538