Skip PositionedMovementLayout when descendants depend on element's height

Source/core/rendering/RenderBlock.cpp

Index: Source/core/rendering/RenderBlock.cpp
diff --git a/Source/core/rendering/RenderBlock.cpp b/Source/core/rendering/RenderBlock.cpp
index bd49f4ad3547517a216814008da89d5912a61957..3528427732d0e58f47274803fcb3b4eaf5a6366c 100644
--- a/Source/core/rendering/RenderBlock.cpp
+++ b/Source/core/rendering/RenderBlock.cpp
@@ -3878,6 +3878,26 @@ bool RenderBlock::recalcOverflowAfterStyleChange()
     return !hasOverflowClip();
 }
 
+// Called when a positioned object moves but doesn't necessarily change size.  A simplified layout is attempted
+// that just updates the object's position. If the size does change, the object remains dirty.
+bool RenderBlock::tryLayoutDoingPositionedMovementOnly()
+{
+    LayoutUnit oldWidth = logicalWidth();
+    LogicalExtentComputedValues computedValues;
+    logicalExtentAfterUpdatingLogicalWidth(logicalTop(), computedValues);
+    // If we shrink to fit our width may have changed, so we still need full layout.
+    if (oldWidth != computedValues.m_extent)
+        return false;
+    setLogicalWidth(computedValues.m_extent);
+    setLogicalLeft(computedValues.m_position);
+    setMarginStart(computedValues.m_margins.m_start);
+    setMarginEnd(computedValues.m_margins.m_end);
+
+    LayoutUnit oldHeight = logicalHeight();
+    updateLogicalHeight();
+    return !hasPercentHeightDescendants() || oldHeight == logicalHeight();
+}
+
 #if ENABLE(ASSERT)
 void RenderBlock::checkPositionedObjectsNeedLayout()
 {