See a review comment for bug 1423013 [1], but it breaks our automation tests, so I am going to handle it in this bug.

Here is a try run [2] to see the broken test cases.

[1] https://phabricator.services.mozilla.com//D15347#418973
[2] https://treeherder.mozilla.org/#/jobs?repo=try&revision=443807b4354abfb21ce421b03631085475af6e1e&selectedJob=221842833

https://treeherder.mozilla.org/#/jobs?repo=try&revision=bab995b7f83c28b548c771be68ec5b4457a9b2d4
Hope no failure happens there. :)

All helper htmls define a viewport meta tag, we should set the pref for safety.

Depends on D18038

This is not a problem at this moment, but in the next commit we are going to
use the minimum scale size for documents which have no overflow:hidden
styles. With the change, helper_touch_action.html starts failing without this
since synthesizeNativeTouchDrag sends events on incorrect positions.

Depends on D18039

Those reftests assume that the content is automatically zoomed in/out but
unfortunately apz.allow_zooming has set to false on Android since bug 1180267.
With the preference value all of the reftests marked as 'fail' in bug 1504659
now succeed.

Though 1133905-{5,6}-v.html and 1133905-{5,6}-v-rtl.html still fail (they've
been failing before bug 1504659), they will be hopefully fixed in bug 1308702.

Depends on D18040

There are two mochitests need to be changed. Both of contents have very large
layout viewport (5000px, 5000px), so when touch drags happen, window.scroll{X,Y}
are not changed at all, now it just moves the visual viewport instead. So we check
visualViewport.offset{Left, Top} in the tests.

Also with this minimum scale size usage change, no-zoom-ref.html doesn't render
the horizontal scrollbar on desktops for some reasons (presumably
reftest-async-zoom affects it, and possibly the reasons are the same as bug
1385145 or bug 1269739). Instead of fixing the issue on desktops, I am going to
take a workaround to add explicit minimum-scale value here, it somehow renders
the scrollbar on desktops too.

Note that the reftet added in this commit fails without this fix.

Depends on D18041

(In reply to Hiroyuki Ikezoe (:hiro) from comment #6)

Created attachment 9040027 [details]
Bug 1520077 - Use the minimum scale size even if no overflow:hidden is specified. r=botond

There are two mochitests need to be changed. Both of contents have very large
layout viewport (5000px, 5000px), so when touch drags happen, window.scroll{X,Y}
are not changed at all, now it just moves the visual viewport instead. So we check
visualViewport.offset{Left, Top} in the tests.

moz-phab doesn't yet update commit messages. I've updated this comment to;

There are two mochitests need to be changed. Both of contents have very large
element (5000px, 5000px), to avoid expanding the layout viewport to the large
size we restrict the minimum scale to 1.0 so that we can still check the layout
scroll range.

https://treeherder.mozilla.org/#/jobs?repo=try&revision=f6574e671b238a1f947dd9e540f95abf6a090b44
test_group_touchevents.html failed on TV, but presumably it's a pre-existing orange (bug 1282638).

https://hg.mozilla.org/mozilla-central/rev/c194c666f232
https://hg.mozilla.org/mozilla-central/rev/6259ce0ef8fa
https://hg.mozilla.org/mozilla-central/rev/1d547e5a7a51