https://bugs.webkit.org/show_bug.cgi?id=273660

<rdar://127270565>

Reviewed by Antti Koivisto.

RenderDeprecatedFlexibleBox marks direct children dirty when dealing with line-clamp, but
since this functionality gets propagated to nested block containers too, we need to make sure
descendant content gets laid out (in order to be able to figure out where to clamp inline content).

* LayoutTests/fast/inline/dynamic-line-clamp-change-on-nested-content-expected.html: Added.
* LayoutTests/fast/inline/dynamic-line-clamp-change-on-nested-content.html: Added.
* Source/WebCore/rendering/RenderBlockFlow.cpp:
(WebCore::RenderBlockFlow::layoutBlock):

Canonical link: https://commits.webkit.org/278384@main

LayoutTests/fast/inline/dynamic-line-clamp-change-on-nested-content-expected.html

@@ -0,0 +1 @@
+PASS

LayoutTests/fast/inline/dynamic-line-clamp-change-on-nested-content.html

@@ -0,0 +1,13 @@
+<style>
+#container {
+  display: -webkit-box;
+  -webkit-box-orient: vertical;
+  overflow: hidden;
+  -webkit-line-clamp: 2;
+}
+</style>
+<div id=container><div>PASS<div>if this is not<div>visible</div></div>
+<script>
+document.body.offsetHeight;
+container.style.webkitLineClamp = "1";
+</script>

Source/WebCore/rendering/RenderBlockFlow.cpp

@@ -452,6 +452,9 @@ void RenderBlockFlow::layoutBlock(bool relayoutChildren, LayoutUnit pageLogicalH
     if (recomputeLogicalWidthAndColumnWidth())
         relayoutChildren = true;
 
+    if (auto* layoutState = view().frameView().layoutContext().layoutState(); layoutState && layoutState->lineClamp())
+        relayoutChildren = true;
+
     rebuildFloatingObjectSetFromIntrudingFloats();
 
     LayoutUnit previousHeight = logicalHeight();