viewport: substitute `document.body.scrollTop` with `window.scrollY` [#80403198]
viewport: substitute `document.body.scrollTop` with `window.scrollY` [#80403198]

How `document.body.scrollTop` property is set specified in the CSSOM
View Module specification. [1] It looks like specification is missing
how user agent should set the property when it is not in quirks
mode. Therefore, user agents apply sixth step about setting the
`scrollTop` attribute of `document.body`. Basically `scrollTop` property
is not set.

Blink, Chromium's rendering engine, is applying second step of getting
`scrollTop` attribute of `document.body` element because when `document`
is not in standards mode and thus skipping the first step.

Seems like other browsers are not returning the value of
`window.scrollY` when getter of `document.body.scrollTop` property is
invoked in standards mode.

Also, I have found a mailing list thread regarding this subject. One
message [2] is pointing out specification is not covering behavior of
`document.body.scrollTop` when user agent is not in quirks mode.

[1] http://dev.w3.org/csswg/cssom-view/#dom-element-scrolltop
[2] http://lists.w3.org/Archives/Public/www-style/2013Oct/0287.html

Signed-off-by: Sonmez Kartal <d2d15c3d37396a5f2a09f8b42cf5f27d43a3fbde@koding.com>

koding/koding,alex-ionochkin/koding,acbodine/koding,rjeczalik/koding,andrewjcasal/koding,koding/koding,cihangir/koding,alex-ionochkin/koding,kwagdy/koding-1,szkl/koding,sinan/koding,jack89129/koding,szkl/koding,acbodine/koding,andrewjcasal/koding,mertaytore/koding,andrewjcasal/koding,mertaytore/koding,andrewjcasal/koding,kwagdy/koding-1,andrewjcasal/koding,andrewjcasal/koding,rjeczalik/koding,cihangir/koding,sinan/koding,rjeczalik/koding,usirin/koding,jack89129/koding,acbodine/koding,koding/koding,sinan/koding,koding/koding,rjeczalik/koding,usirin/koding,gokmen/koding,usirin/koding,koding/koding,mertaytore/koding,alex-ionochkin/koding,usirin/koding,mertaytore/koding,alex-ionochkin/koding,andrewjcasal/koding,cihangir/koding,gokmen/koding,usirin/koding,koding/koding,alex-ionochkin/koding,gokmen/koding,gokmen/koding,koding/koding,jack89129/koding,drewsetski/koding,drewsetski/koding,jack89129/koding,acbodine/koding,sinan/koding,drewsetski/koding,jack89129/koding,szkl/koding,jack89129/koding,rjeczalik/koding,cihangir/koding,usirin/koding,drewsetski/koding,szkl/koding,alex-ionochkin/koding,drewsetski/koding,szkl/koding,mertaytore/koding,alex-ionochkin/koding,rjeczalik/koding,cihangir/koding,cihangir/koding,mertaytore/koding,jack89129/koding,kwagdy/koding-1,gokmen/koding,szkl/koding,alex-ionochkin/koding,mertaytore/koding,andrewjcasal/koding,drewsetski/koding,kwagdy/koding-1,acbodine/koding,cihangir/koding,kwagdy/koding-1,kwagdy/koding-1,gokmen/koding,acbodine/koding,jack89129/koding,kwagdy/koding-1,drewsetski/koding,drewsetski/koding,sinan/koding,gokmen/koding,rjeczalik/koding,sinan/koding,sinan/koding,acbodine/koding,usirin/koding,sinan/koding,szkl/koding,gokmen/koding,koding/koding,acbodine/koding,rjeczalik/koding,mertaytore/koding,szkl/koding,usirin/koding,kwagdy/koding-1,cihangir/koding