Reduce constructor copypasta in RenderText and RenderElement.
<https://webkit.org/b/133056>

Use delegating constructors to remove duplicated initializer lists
from the constructors of RenderText and RenderElement.

Reviewed by Anders Carlsson.

* rendering/RenderElement.cpp:
(WebCore::RenderElement::RenderElement):
* rendering/RenderElement.h:
* rendering/RenderText.cpp:
(WebCore::RenderText::RenderText):
* rendering/RenderText.h:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@169038 268f45cc-cd09-0410-ab3c-d52691b4dbfc