Move MathML type checking virtuals to RenderObject.
<https://webkit.org/b/124111>

Previously, checking the type of a MathML renderer would require
that you first check if it's a RenderMathMLBlock, and then casting
to that type to access the check you really wanted.

This change moves all the isRenderMathMLFoo() virtual functions
to RenderObject. I also made sure all the overloads were private
and marked them OVERRIDE/FINAL as appropriate.

Finally I replaced all the hand-written casting functions with
autogenerated ones using RENDER_OBJECT_TYPE_CASTS.

Reviewed by Anders Carlsson.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@159009 268f45cc-cd09-0410-ab3c-d52691b4dbfc
Use RENDER_OBJECT_TYPE_CASTS for more types.
<https://webkit.org/b/124112>

Generate toRenderFoo() type casting helpers for these classes:

    - RenderCombineText
    - RenderDetailsMarker
    - RenderListMarker
    - RenderVideo
    - RenderView

Reviewed by Anders Carlsson.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@159010 268f45cc-cd09-0410-ab3c-d52691b4dbfc
RenderMathMLFenced should pass around operators in tighter types.
<https://webkit.org/b/124115>

Store operator renderers in RenderMathMLOperator pointers instead
of passing them around as RenderObject.

Reviewed by Martin Robinson.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@159011 268f45cc-cd09-0410-ab3c-d52691b4dbfc
SVGTextMetricsBuilder::walkTree() should take a RenderElement.
<https://webkit.org/b/124105>

Make walkTree() take a RenderElement so we can use the non-virtual
firstChild() internally. All call sites had pointers to compatible
objects already.

Reviewed by Anders Carlsson.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@159012 268f45cc-cd09-0410-ab3c-d52691b4dbfc