Remove Ref(const T&) constructor.
<https://webkit.org/b/121384>

Reviewed by Anders Carlsson.

This constructor was added as a stopgap measure until we got better support
for move semantics in Vector.

* wtf/Ref.h:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@155805 268f45cc-cd09-0410-ab3c-d52691b4dbfc
CTTE: RenderWidgets are never anonymous.
<https://webkit.org/b/121385>

Reviewed by Anders Carlsson.

Codify the following:

- RenderWidget always has an HTMLFrameOwnerElement.
- RenderEmbeddedObject always has an HTMLFrameOwnerElement.
- RenderSnapshottedPlugIn always has an HTMLPlugInImageElement.
- RenderFrame always has an HTMLFrameElement.
- RenderIFrame always has an HTMLIFrameElement.

None of these renderers are ever anonymous, so delete element() and provide
strongly typed reference getters instead.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@155806 268f45cc-cd09-0410-ab3c-d52691b4dbfc
Remove RenderObject::clearNode().
<https://webkit.org/b/121386>

Reviewed by Anders Carlsson.

This was used by ref-counted RenderWidgets after getting removed from their
parent renderer but kept alive by an external ref. We have no need for this
awkward state anymore, so remove clearNode().

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@155807 268f45cc-cd09-0410-ab3c-d52691b4dbfc