Convert RenderFrameSet to LayoutUnits in preparation for turning on subpixel layout

Convert RenderFrameSet to LayoutUnits in preparation for turning on subpixel layout
https://bugs.webkit.org/show_bug.cgi?id=78526

Reviewed by Eric Seidel.

Revert paintColumnBorder and paintRowBorder to IntRect and pixel snap in
paint before calling them. This way the rounding logic is contained in a
single place (in paint).

No new tests, no new functionality.

* rendering/RenderFrameSet.cpp:
(WebCore::RenderFrameSet::paintColumnBorder):
(WebCore::RenderFrameSet::paintRowBorder):
(WebCore::RenderFrameSet::paint):
(WebCore::RenderFrameSet::getCursor):
* rendering/RenderFrameSet.h:
(RenderFrameSet):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@107889 268f45cc-cd09-0410-ab3c-d52691b4dbfc