Fix improper scrollTop/Left usage in LayoutTests/

Rule of thumb here is: if in strict mode, documentElement element
should be used to operate over scrollTop/Left properties.
When in quirks mode, use 'body' element.

CL fixes many layout tests caught by an UseCount/Console warning
being added by https://codereview.chromium.org/26489005/ that
were abusing the relaxed body.scrollTop/Left support Blink currently has.

The exception is LayoutTests/jquery/offset.html, where jQuery on purpose
uses both documentElement and body elements, for cross engine support.

R=Julien Chaffraix, Dan Beam

Review URL: https://codereview.chromium.org/26472003

git-svn-id: svn://svn.chromium.org/blink/trunk@159195 bbb929c8-8fbe-4397-9dbb-9b2b20218538