Bug 1650686 - Drop layout.viewport_contains_no_contents_area. r=botond

I suppose it's been well tested on Fenix.

Differential Revision: https://phabricator.services.mozilla.com/D82305

dom/base/test/test_viewport_metrics_on_landscape_content.html

@@ -12,7 +12,6 @@ SpecialPowers.pushPrefEnv({
   "set": [
     ["apz.allow_zooming", true],
     ["dom.meta-viewport.enabled", true],
-    ["layout.viewport_contains_no_contents_area", true],
   ]
 }, () => {
   // We need to open a new window to avoid running tests in an iframe since

layout/generic/nsGfxScrollFrame.cpp

@@ -509,7 +509,6 @@ bool nsHTMLScrollFrame::TryLayout(ScrollReflowInput* aState,
   // minimum-scale is changed to the original one, and so forth.
   if (mHelper.UsesOverlayScrollbars() && mHelper.mIsUsingMinimumScaleSize &&
       mHelper.mMinimumScaleSize.height > overflowRect.YMost()) {
-    MOZ_ASSERT(StaticPrefs::layout_viewport_contains_no_contents_area());
     overflowRect.height +=
         mHelper.mMinimumScaleSize.height - overflowRect.YMost();
   }
@@ -6007,14 +6006,6 @@ void ScrollFrameHelper::UpdateMinimumScaleSize(
   // to be the minimum scale.
   mMinimumScaleSize = CSSSize::ToAppUnits(ScreenSize(displaySize) / minScale);
 
-  // Clamp the min-scale size so it's not taller than the content height.
-  // TODO: Bug 1571599: Drop this check.
-  if (!StaticPrefs::layout_viewport_contains_no_contents_area()) {
-    mMinimumScaleSize =
-        Min(mMinimumScaleSize,
-            nsSize(aScrollableOverflow.XMost(), aScrollableOverflow.YMost()));
-  }
-
   // Ensure the minimum-scale size is never smaller than the ICB size.
   // That could happen if a page has a meta viewport tag with large explicitly
   // specified viewport dimensions (making the ICB large) and also a large

layout/reftests/meta-viewport/reftest.list

@@ -15,12 +15,12 @@ defaults pref(dom.meta-viewport.enabled,true) pref(apz.allow_zooming,true)
 == no-scalable-with-minimum-scale.html no-scalable-with-minimum-scale-ref.html
 == clamped-by-default-minimum-scale.html initial-scale-0_25-ref.html
 == position-fixed-on-half-height-content.html position-fixed-on-half-height-content-ref.html
-pref(layout.viewport_contains_no_contents_area,true) == position-fixed-on-landscape-content.html position-fixed-on-half-height-content-ref.html
-pref(layout.viewport_contains_no_contents_area,true) == position-fixed-on-square-content.html position-fixed-on-square-content-ref.html
-pref(layout.viewport_contains_no_contents_area,true) == async-scroll-to-no-content-area.html async-scroll-to-no-content-area-ref.html # bug 1571623 to track down the failure on WebRender
-pref(layout.viewport_contains_no_contents_area,true) == resolution-change-on-landscape-content.html resolution-change-on-landscape-content-ref.html
+== position-fixed-on-landscape-content.html position-fixed-on-half-height-content-ref.html
+== position-fixed-on-square-content.html position-fixed-on-square-content-ref.html
+== async-scroll-to-no-content-area.html async-scroll-to-no-content-area-ref.html # bug 1571623 to track down the failure on WebRender
+== resolution-change-on-landscape-content.html resolution-change-on-landscape-content-ref.html
 == scrollbars-in-half-height-content.html scrollbars-in-half-height-content-ref.html
-pref(layout.viewport_contains_no_contents_area,true) == scrollbars-in-landscape-content.html scrollbars-in-landscape-content-ref.html
+== scrollbars-in-landscape-content.html scrollbars-in-landscape-content-ref.html
 
 skip-if(!Android) == position-fixed-on-minimum-scale-size.html position-fixed-on-minimum-scale-size-ref.html
 == position-fixed-out-of-view.html about:blank
@@ -28,13 +28,13 @@ skip-if(!Android) == position-fixed-on-minimum-scale-size.html position-fixed-on
 == overflow-region.html overflow-region-ref.html
 == overflow-hidden-region.html overflow-region-ref.html
 == overflow-hidden-region-with-negative-left-positioned-element.html overflow-region-ref.html
-pref(layout.viewport_contains_no_contents_area,true) == horizontal-overflow-hidden-region.html horizontal-overflow-hidden-region-ref.html
+== horizontal-overflow-hidden-region.html horizontal-overflow-hidden-region-ref.html
 == vertical-overflow-hidden-region.html about:blank
 == scroll-to-unreachable-area.html scroll-to-unreachable-area-ref.html
 == wrapped-text-at-icb.html wrapped-text-at-icb-ref.html
 == overflow-hidden-region-dynamic-width-change.html overflow-region-ref.html
 == remove-overflow-hidden-region.html remove-overflow-hidden-region-ref.html
-pref(layout.viewport_contains_no_contents_area,true) == dynamic-grow-width.html horizontal-overflow-hidden-region-ref.html
+== dynamic-grow-width.html horizontal-overflow-hidden-region-ref.html
 == dynamic-grow-width-and-height.html overflow-region-ref.html
 == not-able-to-scrollTo.html about:blank
 == min-scale-aspect-ratio.html about:blank

modules/libpref/init/StaticPrefList.yaml

@@ -6444,13 +6444,6 @@
   value: 1
   mirror: always
 
-# Whether we expand the layout viewport even if the expanded viewport doesn't
-# contain any contents in the area.
-- name: layout.viewport_contains_no_contents_area
-  type: bool
-  value: true
-  mirror: always
-
 # Test only.
 - name: layout.dynamic-toolbar-max-height
   type: RelaxedAtomicInt32