browserElement_ScrollEvent.js is affected by this change. Before this change
the document for iframe mozbrowser was not considered as the root content
document, but after this change, it's considered as the root content document.
Given the nature of iframe mozbrowser, I believe it's the right behavior.
The browser mochitest in this commit fails without this change since
the minimum-scale size is used in the out-of-process iframe so that the visual
viewport size gets 3x bigger than the expected size.
Differential Revision: https://phabricator.services.mozilla.com/D36547
--HG--
extra : moz-landing-system : lando
Hiroyuki Ikezoe