Position replaced elements on pixel bounds

Position replaced elements on pixel bounds
https://bugs.webkit.org/show_bug.cgi?id=90354

Reviewed by Eric Seidel.

To avoid sizing and repaint issues we should layout replaced elements on
pixel bounds. We already ensure that replaced elements are sized in full
pixels and that they are painted on pixel bounds. By also ensuring that
they are placed on pixel bounds we avoid pixel having the size be
expanded by pixel snapping and repainting/invalidation rect issues when
scrolling.

Test: fast/repaint/repaint-during-scroll-with-zoom.html

* rendering/RenderBox.cpp:
(WebCore::RenderBox::computePositionedLogicalWidthReplaced):
(WebCore::RenderBox::computePositionedLogicalHeightReplaced):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@121722 268f45cc-cd09-0410-ab3c-d52691b4dbfc