Duolingo continue/next bar trails off of viewport

https://bugs.webkit.org/show_bug.cgi?id=273526
<rdar://126777425>

Reviewed by Antti Koivisto.

When a box changes containing block through style mutation (e.g. by going from out-of-flow to inflow),
its (grid/flex driven) override value becomes stale.
(note that these override values are apparently sticky and we have to keep them around in-between layouts
for example to be able to resolve percent padding values for getComputedStyle)

* LayoutTests/fast/dynamic/out-of-flow-going-in-flow-inside-grid-expected.html: Added.
* LayoutTests/fast/dynamic/out-of-flow-going-in-flow-inside-grid.html: Added.
* Source/WebCore/rendering/RenderGrid.cpp:
(WebCore::RenderGrid::layoutPositionedObject):

Canonical link: https://commits.webkit.org/278209@main

LayoutTests/fast/dynamic/out-of-flow-going-in-flow-inside-grid-expected.html

@@ -0,0 +1,8 @@
+<style>
+div {
+  width: 400px;
+  height: 300px;
+  background-color: green;
+}
+</style>
+<div></div>

LayoutTests/fast/dynamic/out-of-flow-going-in-flow-inside-grid.html

@@ -0,0 +1,22 @@
+<style>
+.grid {
+  width: 200px;
+
+  display: grid;
+  padding: 100px;
+  position: relative;
+  background-color: green;
+}
+
+#abs {
+  position: absolute;
+  background-color: green;
+  width: 100%;
+  height: 100px;
+}
+</style>
+<!-- PASS if in-flow leaf does not stick out of grid container -->
+<div class=grid><div><div id=abs><script>
+document.body.offsetHeight;
+abs.style.position = "static";
+</script>

Source/WebCore/rendering/RenderBox.cpp

@@ -391,6 +391,9 @@ void RenderBox::styleDidChange(StyleDifference diff, const RenderStyle* oldStyle
     // any override content size set by our container, because it would likely be incorrect after the style change.
     if (isOutOfFlowPositioned() && parent() && parent()->style().isDisplayFlexibleBoxIncludingDeprecatedOrGridBox())
         clearOverridingContentSize();
+
+    if (oldStyle && oldStyle->hasOutOfFlowPosition() != style().hasOutOfFlowPosition())
+        clearOverridingContainingBlockContentSize();
 }
 
 void RenderBox::updateGridPositionAfterStyleChange(const RenderStyle& style, const RenderStyle* oldStyle)